High Ambient (Desert) Temps Kills HVB Performance (MPGs)

[Hybrider]

Now that we have reached summer temperatures (85°-110° for the daily range) here in the desert in Arizona, I have seen my HVB performance (and MPGs) go way down hill from what it was before. But now that the ambient temps are mostly above 90° from the get-go early in the morning and right around 105°-110° for my commute home, I can see my HVB takes much longer to charge and loses its charge much faster now at the same consistent highway speeds of 65 MPH that I always drive on the highway (speed limit of 65) during my commute.

 

I have seen comments in this forum about the MPG decrease at increased temps for the FFHs being due to the A/C running, but I have previously easily achieved 47-49 MPG (mostly freeway) when running the A/C at the lowest fan level when the daily temps were in the 65°-90° range.

 

I am still able to run the A/C at the lowest fan level most of the time even when the temps are between 100° and even 110°, so that doesn't seem to be cause of my decreased MPG. Whereas I was getting 47-49 MPG previously with the A/C running, I am getting more like 43-45 MPG, a dramatic drop to me, seemingly due to just the increased temps here in AZ. I don't even want to see what happens to my FE when we start getting up to the 115°-119° highs that we get frequently here in the hottest part of the summer.

 

The Tesla website has a really cool range calculator where you can input your typical driving conditions. And if you input the summer temps we typically see in AZ in the summer, you will see their single-charge range drops dramatically with desert summer temps, probably more of a drop in range than if I were to drive their car at 75 or 80 MPH instead of my now-typical 65 MPH.

 

Also another thing I have noticed here in Arizona, due to having warmer temps than everywhere else in the country, is that the EV+ mode is basically useless for me, since my car just about always starts up in EV (silent) mode. In fact, it wasn't until recently when we reached summer temps here that my FFH would ever start up with the ICE immediately, and that seems to be mostly due to my HVB discharging so rapidly on the road and even discharging some while the car is off, seemingly due to the temperatures hovering around 100°-110° for most of the day.

 

I was wondering if anyone in the Southwest desert region of the country has ever tried using the ScanGauge to confirm this gut-feel that I have about the HVB performance at temps above 100° having such an impact on the HVB performance at these extremely high summer temps.

 

And summer in AZ sucks for a FFH owner, but so far not nearly as bad as it seemed to suck for those in the cold, cold winter up North this past winter, and I'm hoping it stays that way for the rest of the summer here.

 

I know, I know...I shouldn't worry about this small percentage decrease in MPGs, since I am still getting super MPGs and loving every minute of it. But I just wanted to share my experiences about high temps affecting my HVB performance, and whine a little bit about it since I was getting such great fuel economy before the high temps hit, and with very little effort on my part (as I was already driving my previous 2004 Buick Century like a granny). And it is a bit depressing to see my lifetime MPG average starting to go down for the very first time ever in the 3500 miles (4 months of ownership) I have put on my glorious, fabulous FFH.

 

I love it when others on this forum gleam and gloat about the goodness of the FFHs, and I have no choice but to do so too. Sometimes I really feel like Ford designed my SE configuration of the FFH specifically targeted at me, since it is a top-of-the-line, full hybrid, packed into a luxuriously-comfortable mid-size sedan, and that looks so totally sporty and awesome on top of all of that techy greatness. Whoo-hoo for FFHs and FFH owners!!! :yahoo: :worship:

[GrySql]

I agree with you, I live in a hot (but, it's a dry heat!) climate too, not far from Palm Springs, CA. Coming home from my 4,000 mile trip 3 weeks ago as soon as the temps approached 90F my mpg's began dropping down. I'd had the A/C on for a 1,000 miles prior without as big a drop as the high ambient temps gave me.

As I drove thru AZ and westward on I-10 the temps got to 109F and my mpg's were at their worst. I wasn't paying attention to my HVB, just wanting to get home, but that is a very good assumption on your part.

 

I hope Lolder will explain it to us - again. I forget the math stuff easily these days.

 

Your comment makes sense about the Tesla that we passed near Quartzite, AZ, he was going 60mph in a 75mph zone.

We like our car too.

Edited June 9, 2014 by GrySql

[hybridbear]

Have you paid attention to your A/C kW power draw on the MyView screen? Even with the fan on the lowest setting the compressor might be working harder & thus consuming more electricity in the higher temps.

 

How cool does it get at night? Are you parked in the hot sun all day?

 

The HVB will limit how quickly it can be charged & discharged at high temps. Normally for the FFH the Max Charge Limit and Max Discharge Limit are equal, 35 kW. In very cold temps and very hot temps the car will reduce those numbers. It's possible that you're seeing some of that which is causing the ICE to run more and thus lowering your MPG. You could also be getting less regenerative braking if the HVB Max Charge Limit is less than 35 kW which would lead to lower MPG. The Energi vehicles will force the car into Hybrid mode even with a full HVB if the HVB temp is too high. The FFH will limit the use of the HVB if its temp is too high.

 

Now that we have reached summer temperatures (85°-110° for the daily range) here in the desert in Arizona, I have seen my HVB performance (and MPGs) go way down hill from what it was before. But now that the ambient temps are mostly above 90° from the get-go early in the morning and right around 105°-110° for my commute home, I can see my HVB takes much longer to charge and loses its charge much faster now at the same consistent highway speeds of 65 MPH that I always drive on the highway (speed limit of 65) during my commute.

 

I have seen comments in this forum about the MPG decrease at increased temps for the FFHs being due to the A/C running, but I have previously easily achieved 47-49 MPG (mostly freeway) when running the A/C at the lowest fan level when the daily temps were in the 65°-90° range.

 

I am still able to run the A/C at the lowest fan level most of the time even when the temps are between 100° and even 110°, so that doesn't seem to be cause of my decreased MPG. Whereas I was getting 47-49 MPG previously with the A/C running, I am getting more like 43-45 MPG, a dramatic drop to me, seemingly due to just the increased temps here in AZ. I don't even want to see what happens to my FE when we start getting up to the 115°-119° highs that we get frequently here in the hottest part of the summer.

 

The Tesla website has a really cool range calculator where you can input your typical driving conditions. And if you input the summer temps we typically see in AZ in the summer, you will see their single-charge range drops dramatically with desert summer temps, probably more of a drop in range than if I were to drive their car at 75 or 80 MPH instead of my now-typical 65 MPH.

 

Also another thing I have noticed here in Arizona, due to having warmer temps than everywhere else in the country, is that the EV+ mode is basically useless for me, since my car just about always starts up in EV (silent) mode. In fact, it wasn't until recently when we reached summer temps here that my FFH would ever start up with the ICE immediately, and that seems to be mostly due to my HVB discharging so rapidly on the road and even discharging some while the car is off, seemingly due to the temperatures hovering around 100°-110° for most of the day.

 

I was wondering if anyone in the Southwest desert region of the country has ever tried using the ScanGauge to confirm this gut-feel that I have about the HVB performance at temps above 100° having such an impact on the HVB performance at these extremely high summer temps.

 

And summer in AZ sucks for a FFH owner, but so far not nearly as bad as it seemed to suck for those in the cold, cold winter up North this past winter, and I'm hoping it stays that way for the rest of the summer here.

 

I know, I know...I shouldn't worry about this small percentage decrease in MPGs, since I am still getting super MPGs and loving every minute of it. But I just wanted to share my experiences about high temps affecting my HVB performance, and whine a little bit about it since I was getting such great fuel economy before the high temps hit, and with very little effort on my part (as I was already driving my previous 2004 Buick Century like a granny). And it is a bit depressing to see my lifetime MPG average starting to go down for the very first time ever in the 3500 miles (4 months of ownership) I have put on my glorious, fabulous FFH.

 

I love it when others on this forum gleam and gloat about the goodness of the FFHs, and I have no choice but to do so too. Sometimes I really feel like Ford designed my SE configuration of the FFH specifically targeted at me, since it is a top-of-the-line, full hybrid, packed into a luxuriously-comfortable mid-size sedan, and that looks so totally sporty and awesome on top of all of that techy greatness. Whoo-hoo for FFHs and FFH owners!!! :yahoo: :worship:

[Waldo]

Forcing your climate system to the lowest fan setting is like tying a hand behind it's back. The A/C compressor is a variable unit, so it will adjust it's output/power consumption depending on how cold you have it set. If you force the fan to the lowest setting, it will have to run the compressor at max power to keep the evaporator cold enough to make the low airflow work. Basically more airflow over a warmer evaporator will give you the same result as less airflow over a colder evaporator (older cars with fixed compressors can't do this, they can only get the evaporator to one temperature). My suggestion would be to leave the fan in auto mode and just set the temperature higher. That way the system is free to work in the most efficient way it can.

[acdii]

The Lithium Ion batteries in our cars are susceptible to overheating, and charging/discharging them produces heat. The temp of the pack needs to be under a certain range in order to protect the cells from damage. Since the cooling system uses the cabin air to cool it down, keeping the temps in the cabin lower may help keep the pack cooler. This is why hot temps reduce MPG in the FFH, the computer is protecting the batteries from heat damage.

[Eddie Sessum]

Forcing your climate system to the lowest fan setting is like tying a hand behind it's back. The A/C compressor is a variable unit, so it will adjust it's output/power consumption depending on how cold you have it set. If you force the fan to the lowest setting, it will have to run the compressor at max power to keep the evaporator cold enough to make the low airflow work. Basically more airflow over a warmer evaporator will give you the same result as less airflow over a colder evaporator (older cars with fixed compressors can't do this, they can only get the evaporator to one temperature). My suggestion would be to leave the fan in auto mode and just set the temperature higher. That way the system is free to work in the most efficient way it can.

 

 

What you set everything on has nothing to do with the compressor... It has set pressures that it operates most efficiently at and it will spin itself up and down depending where it needs to be to keep those pressures. Even with the temp set on low if you turn the fan all the way down it doesn't have to work anywhere near as hard to keep those pressures.

[corncobs]

 

 

What you set everything on has nothing to do with the compressor... It has set pressures that it operates most efficiently at and it will spin itself up and down depending where it needs to be to keep those pressures. Even with the temp set on low if you turn the fan all the way down it doesn't have to work anywhere near as hard to keep those pressures.

I don't believe this is true because if you change temp and fan manually the load from A/C ( climate ) goes way down.

[Eddie Sessum]

I don't believe this is true because if you change temp and fan manually the load from A/C ( climate ) goes way down.

 

 

Because when you change the fan speed manually it can go slower to cool the same. You just said what I said in another way lol. Where as a gas car the compressor cycles based on pressures ours slows down. Fan speed and inside the car temp are the 2 things that will effect this unless you have a mechanical failure of the electric fan under the hood

[Waldo]

 

 

What you set everything on has nothing to do with the compressor... It has set pressures that it operates most efficiently at and it will spin itself up and down depending where it needs to be to keep those pressures. Even with the temp set on low if you turn the fan all the way down it doesn't have to work anywhere near as hard to keep those pressures.

 

I think you're missing my point. The climate system works to maintain evaporator temperatures, it doesn't really care what pressure is needed to achieve those temperatures. On a traditional A/C system it has to cycle to maintain those temps, but on the FFH (and most other new Fords now) it can vary the displacement of the compressor to allow variation of the evap temperature. My point is that when you reduce the fan speed but maintain a low set temperature, the system will decide it needs a lower evap temperature and will thus run the compressor harder to achieve that. Of course running the fan at high speed will also bring up the temperature of the evaporator, requiring higher loads from the compressor just to maintain the evap temp. Somewhere in the middle is the optimum point for efficiency, which is why my advice was to leave it in auto because the computer can find that optimum point better than you can.

[acdii]

I just wish the compressor could be shut off when in defrost mode. When its in the 50's and you need to defog the windshield, it can get mighty cold in there.

[hybridbear]

 

I think you're missing my point. The climate system works to maintain evaporator temperatures, it doesn't really care what pressure is needed to achieve those temperatures. On a traditional A/C system it has to cycle to maintain those temps, but on the FFH (and most other new Fords now) it can vary the displacement of the compressor to allow variation of the evap temperature. My point is that when you reduce the fan speed but maintain a low set temperature, the system will decide it needs a lower evap temperature and will thus run the compressor harder to achieve that. Of course running the fan at high speed will also bring up the temperature of the evaporator, requiring higher loads from the compressor just to maintain the evap temp. Somewhere in the middle is the optimum point for efficiency, which is why my advice was to leave it in auto because the computer can find that optimum point better than you can.

I did some testing of this today. Once the AC had cooled the car completely and was just maintaining the temp I tried adjusting the fan speed down to the lowest setting rather than leaving it on Auto. Doing so did not result in an increase in the Watts consumed by the AC unit. However, lowering the fan speed resulted in less Watts flowing through the DCDC converter to power the fan which reduced total energy consumption from the AC. I will have to perform further testing in the future to confirm that the AC watts consumed really doesn't increase.

[lolder]

If you have the AC set at Auto 72, the energy required to cool from 100 is twice what is required at 86. Running the fan on low WILL lower the compressor load as with less airflow over the evaporator, you need less cooling. The system maintains a minimum evaporator temperature regardless of what you set the cabin temperature at. When you select lower fan speeds, you increase the time to cool down the car. Take your choice. The system probably works best all around in Auto. It's a driving distraction to fiddle with the controls. The compressor is on in defrost with most cars to dehumidify. The 2010 FFH defrosts/defogs automatically without selecting defrost. There's a humidity sensor that diverts air to the windshield vents, ( I think ).

[Eddie Sessum]

 

I think you're missing my point. The climate system works to maintain evaporator temperatures, it doesn't really care what pressure is needed to achieve those temperatures. On a traditional A/C system it has to cycle to maintain those temps, but on the FFH (and most other new Fords now) it can vary the displacement of the compressor to allow variation of the evap temperature. My point is that when you reduce the fan speed but maintain a low set temperature, the system will decide it needs a lower evap temperature and will thus run the compressor harder to achieve that. Of course running the fan at high speed will also bring up the temperature of the evaporator, requiring higher loads from the compressor just to maintain the evap temp. Somewhere in the middle is the optimum point for efficiency, which is why my advice was to leave it in auto because the computer can find that optimum point better than you can.

 

 

Evaporator temperature is based on the pressures also. There is a charge that will tell you what pressures cause what temperatures at the evaporator and condensor for 134a. Look it up.

[Eddie Sessum]

http://www.csgnetwork.com/r134apresstempconv.html

 

 

Pressures shown can be used on high or low side. It tells you what the temp of the freon is at those temps. High side is outside and thats where the airflow cools it to lower the pressure (pressure change from high to low makes it get ice cold)

[Waldo]

You guys are still missing my point. From the shop manual:

 

Instead of cycling on and off like a traditional A/C compressor, the SOBDMC monitors the evaporator temperature from the FCIM to raise or lower the A/C electric compressor speed as required.

 

There is no "minimum temperature" in the evaporator. The computer can control the temperature over a range. it will adjust that range based on the temperature setting and the interior cabin temperature readings. So if the interior temp is hotter than your setting, it will do everything possible to cool the car. If you've manually controlled the fan speed to a low setting, it will lower the temperature of the evaporator as much as it can.

 

hybridbear, your test is only valid if it's hot enough that the system can't maintain the temperature at the lower fan settings. Try it again but do it while it's trying to cool the car, in other words, when the Auto would normally have the fan on 4 or 5 bars.

 

Remember my theory here is that you are more efficient to run at a setting of say 75 in full auto vs a setting of 72 at low fan, when the conditions mean that you end up with the same interior temp. In other words, you need conditions where 72 at low fan does not bring the car down to 72, it can only keep it around 75.

[lolder]

Evaporators are usually held to 40-50 º F so they don't freeze the moisture so there is a limit. Higher fan speed and higher ambient interior temperatures make the compressor run harder to keep the evaporator temperature relatively constant.

[Waldo]

Evaporators are usually held to 40-50 º F so they don't freeze the moisture so there is a limit. Higher fan speed and higher ambient interior temperatures make the compressor run harder to keep the evaporator temperature relatively constant.

 

Still missing the point. The Fusion, and almost all of the new Fords, actively control the evaporator temperature through software. If the computer wants the evaporator at 40 degrees it can do that. If it wants it at 50 degrees, it can do that. It's not like the traditional systems where evaporator temperatures are the results of the pressure and cycling the compressor is the only method to control it. Now it's the pressures that are the result of the desired evaporator temperature.

[Eddie Sessum]

The electric compressors are different. The regular cars with belt driven compressors control that by mixing warm air. Any person with normal hearing can stand next to a new ford and hear the compressor cycling when it hits a certain pressure.

 

Basicly what we have is similar to a dual stage home air conditioner, which when its not needed because the car cools off enough it slows the speed down.

 

 

At night i can put my temp on low and turn the fan to full speed max ac and it wont go above 2 lines on power consumption. Because the pressures dont require it. In your theory a 80* car inside on low temp and fan all the way up it should run full speed. hybrid even said that this isnt the case. Go look at the ac power pull on your car, i guess its lying right?

[Hybrider]

Have you paid attention to your A/C kW power draw on the MyView screen? Even with the fan on the lowest setting the compressor might be working harder & thus consuming more electricity in the higher temps.

 

How cool does it get at night? Are you parked in the hot sun all day?

 

...

Over the course of several days, I have monitored the A/C power draw on the MyView gauge, and the behavior was not at all what I had expected to see.

 

So to begin with, the A/C power draw data for in the morning when I leave for work, when the temps are in the 85°-93° range in my garage (outside temp is actually around 75°-80°), the A/C power draw climbs immediately to about 2.5 kW, no matter whether I am in complete "Auto" mode or in semi-manual mode or in Max A/C mode. It stays at that initial maximum draw for only about 1-2 minutes, and then over the course of about another 1 minute, it drops to a final level fluctuating between 0.4-0.6 kW, and stays at the same low level for rest of the duration of my 30 minute commute. Even if I change the temp or fan speed or air flow path, there is no effect on the A/C power draw, no matter whether I am at the initial high draw or at the final low draw. This was the surprising part for me.

 

Now if I change to Max A/C mode after reaching the final low draw (0.4-0.6 kW), there will be no immediate effect on the A/C power draw. But after about 1 minute, the power draw will very gradually start climbing, and after several minutes of this Max A/C mode, when I can no longer stand it anymore due to the excessive noise, air flow, and coolness, it has only increased the power draw by about 1 kW to about 1.5 kW. I don't know if power draw while in Max A/C mode would keep climbing since I am not able to endure the Max A/C mode any longer after I have reached my limits of endurance.

 

So now for the A/C power draw data for my return trip from work, when the ambient temps are at true desert-level temps. For my drive home from work, when the outside temp is around the 107°-110°, and with my FFH having been parked in the shade, the power draw curve over time is basically the same as I mentioned before, with the max power draw peak being immediately as soon as I turn the A/C on, and the final low power draw being reached a few minutes later. But the difference during these afternoon high temps of the day is that the max initial power draw is about 3.5 kW for about 2-4 minutes, and then the final low draw is slightly higher, fluctuating between 0.6-0.8 kW.

 

The A/C power draw behavior I saw when I have been parked in the sun at 105° is that the peak draw was around 4.5-5 kW for about 2-4 minutes, and the final low draw was the same 0.6-0.8 kW draw that I saw when I started with my FFH in the sshade.

 

To reiterate, I basically saw no difference in the power draws that I saw over the course of several days that could be directly attributable to the varying A/C modes that I had selected. The only variable that seemed to affect the A/C power draws, whether it be the initial peak draw or the final leveled-off draw was the temp inside the car, which was directly correlated to the outside temp and whether my FFH was parked in the sun or in the shade. I monitored the A/C power draw while using various climate control settings, including "Auto" mode with various temp settings between 72° and 80°, and including various semi-auto settings, by changing the fan speed, the air distribution settings, along with changing the set temps, and even using Max A/C, and I did not see any immediate change in the A/C power draw when I changed any of those settings. As I mentioned, the only time I did see any change in power draw was when I left the climate control on Max A/C mode for several minutes after reaching the final low levels, and it would only increase by about 1 kW above the final low draw.

 

Anotber new-to-me observation I have noticed is that there does not seem to be any truly manual mode with my 2014 FFH climate control system since the temp setting is always involved to some degree or another in a semi-auto fashion. Even when the fan is set to a manual, user-specified speed and the air distribution setting is set to a manual, user-specified air vent selection. I have not found any way to not have the temp setting involved in some way, since it always seems to change the output air temp to its own volition.

 

So here is a table summarizing the A/C power draw data, for desert ambient temps, that I have detailed above.

 

Initial Park Condition and Ambient Temp

---------------------------------------------

Shade, 85°-93° Shade, 107°-110° Sun, 105°

-------------- ---------------- -----------

Initial Peak Draw 2.5 kW 3.5 kW 4.5-5 kW

Duration of Peak Draw 1-2 minutes 2-4 minutes 2-4 minutes

Final Draw 0.4-0.6 kW 0.6-0.8 kW 0.6-0.8 kW

 

So based on my findings and comments from others in this forum, my BKM (Best-Known Method) that I use now is that I start my summer desert trips in Auto mode, with an initial temp setting of 80°, and then when I start feeling too warm due to the decreasing air temps being output through the mid-level dash vents, I will then drop the temp setting by about 1-2° at a time, which usually eventually ends up stablilizing on a setting in the 74°-76° range. Then, at my final selected auto temp settiing, if my eyes start getting too dried out from the air coming out of the mid-level dash vents, located on either side of the steering wheel which I always leave positioned directly at my face, then I switch the air distribution to be dash vents (middle level) and defrost vents (upper level), thereby being a semi-auto setting.

 

And then I rinse and repeat at the beginning of the next day.

[mwr]

Would you conclude from that testing that A/C on Auto works at least as well as any other method for cooling and low power consumption?

[Eddie Sessum]

You will notice that the maximum power consumption is software limited based on outside temp. You may be seeing part of that. Have you seen the little + sign pop-up next to the 5 yet? I saw it for the first time today as my car was in the sun and until I drove for a few min the outside temp above above 100. I believe this was part of the fuel economy program that changed the ac up. Basing off outside Temps.

[Hybrider]

Would you conclude from that testing that A/C on Auto works at least as well as any other method for cooling and low power consumption?

Actually no, since you just reminded me of other datapoints that I didn't remember until now. When I set my climate control manually to the lowest fan setting, I did notice a lower initial power draw, where the A/C power draw in the morning was 1.5 kW versus 2.5 kW when I had set the temp to 80° in auto mode.

 

So here is a new, revised summary table, including those tidbits of data I just mentioned:

 

Initial Park Condition and Ambient Temp

---------------------------------------------

Low Fan, Shade, 85°-93° Shade, 85°-93° Low Fan, Shade, 107°-110° Shade, 107°-110° Sun, 105°

----------------------- -------------- ------------------------- ---------------- -----------

Initial Peak Draw 1.5 kW (manual) 2.5 kW (auto) 2.5 kW (manual) 3.5 kW (auto) 4.5-5 kW (auto)

Duration of Peak Draw 1-2 minutes 1-2 minutes 2-4 minutes 2-4 minutes 2-4 minutes

Final Draw 0.4-0.6 kW 0.4-0.6 kW 0.6-0.8 kW 0.6-0.8 kW 0.6-0.8 kW

Edited June 20, 2014 by Hybrider

[mwr]

That initial power draw is for such a short duration that my tendency would be to just use Auto. That wold cool the car faster and use very little more fuel (i think).

[Hybrider]

Actually no, since you just reminded me of other datapoints that I didn't remember until now. When I set my climate control manually to the lowest fan setting, I did notice a lower initial power draw, where the A/C power draw in the morning was 1.5 kW versus 2.5 kW when I had set the temp to 80° in auto mode.

 

So here is a new, revised summary table, including those tidbits of data I just mentioned:

 

Initial Park Condition and Ambient Temp

---------------------------------------------

Low Fan, Shade, 85°-93° Shade, 85°-93° Low Fan, Shade, 107°-110° Shade, 107°-110° Sun, 105°

----------------------- -------------- ------------------------- ---------------- -----------

Initial Peak Draw 1.5 kW (manual) 2.5 kW (auto) 2.5 kW (manual) 3.5 kW (auto) 4.5-5 kW (auto)

Duration of Peak Draw 1-2 minutes 1-2 minutes 2-4 minutes 2-4 minutes 2-4 minutes

Final Draw 0.4-0.6 kW 0.4-0.6 kW 0.6-0.8 kW 0.6-0.8 kW 0.6-0.8 kW

And now after remembering that, I think I need to change my BKM to start with a semi-manual setting with a low fan setting at 80°, and then after I reach the final low-draw condition, I can then switch back to the Auto mode.

[Hybrider]

That initial power draw is for such a short duration that my tendency would be to just use Auto. That wold cool the car faster and use very little more fuel (i think).

That is actually part of my point, is that the initial high power draw is for such a short time, that I don't think it really matters what climate control settings you choose, since the ambient temps will be the major deciding factor for A/C power draws. And even with those differences in power draws for the excessively high temps, the real contributor IMHO is the excessive heat decreasing the charging and charge-maintainability of the HVB, which is the emphasis I was trying to impart when I started this topic to begin with.