It gets hotter down here, and it's easy enough to do. I figured a lot of people are probably not aware that they can even check the electrolyte level, and with all these battery problems, maybe it's a factor.

Same here. I posted about it but got zero respone . After seeing this Battery TSB , I figured it must be sand they put down when it snows coming up via the battery air intake duct.

 

Good find, I hadn't read that particular TSB. I will have to remember that airflow positioning info when I put the battery back in . . . All kinds of stuff could get forced in through that air vent at speed I suppose, never noticed it. I don't drive the 8 in winter so it's just crud flying around in summer. I noticed that I also get a lot of grit lying on all those covers in the engine compartment also. With everything so pristine and black that stuff shows up well. My other cars have just engines and no Tupperware collections under the hood so I wouldn't notice the dirt in them as easily :-)

 

Scoop, I don't want to beat a dead horse, but I emailed the author at Canadian Driver with your views on the trickle charger as a battery heating method.
I thought I would share his response with you. It's all greek to me and all I know is the both of you are much better at numbers than I am.
Here is his response:

"Thank you for forwarding the web site comments from the RX8 site and your defense of my information. I looked at all the calculations and was a bit overwhelmed as I haven't had to do much of that since high school but I did immediately see several errors in the writers assumptions. Here is a rough outline:

First, a trickle charger provides usually more than 14 volts and the article stated a 2 amp charger. I will go half way and allow 1.5 amps. That would provide 21 watts of power. I am not sure where the writer guesses 50% goes into charging and 50% is waste heat. Charging causes a chemical reaction which generates heat. The waste heat also heats the battery so theoretically, all or most of it is converted to heat. Never the less, I will use his 50% figure. That would give 21 watts X 50% = 10.5 watts X 3.41 watts per btu to = 35.8 BTU. ( considerably higher than his calculations.

His next major error in in the weight of liquid in a battery. He uses 31.225 lb.. According to the Exide battery replacement chart for a 1996 Chev pickup truck, the battery total weight is only 43 lbs! Most of the weight is in lead compounds!. Experience filling new batteries with electrolyte lets me estimate that only about one pint of fluid is in a battery. Even if it was one quart, the weight would be 10 lbs per gallon ( SG of water) divided by 4 X SG of electrolyte of 1.228 = just over 3 lbs of liquid. (much less that the 31 lbs of liquid the writer uses!!!!)

If I use his formula the battery temperature increases 35.8 BTU / 3 lbs liquid = +12 degrees (rounded off) temperature increase per hour. He calculated only .71F degrees. I know that there is more to warm up than just the liquid but even if I halved my calculations, the heating is far more than the writer deduced.

On to heat loss: Battery surface area is not 4 sq. ft. Using the Exide Battery figures of 10.3 inches X 6.9 inches X 7.8 inches, the battery surface area is only 2.9 square feet. I have no knowledge of the insulating qualities or factors of the battery case but I do know that the internal area of the battery has to transfer heat to the outside and the transfer is slower than that through glass. Also, most auto manufacturers position the battery to shield it, with foam wraps, plastic covers and or location in a small area that would provide additional insulation value to the battery heat loss. Even if I used the writer's calculations of 2.11 degrees F heat loss per hour ( which are not correct because of the wrong surface area), you can see that there is more heat going into the battery than escaping.

Finally, I have never sat down and done all these calculations before. My statements on heat gain are based on years of repairing cars in cold Saskatchewan winters (-40 degree days are not uncommon). I know that you can physically feel the temperature difference of a battery if it has had a trickle charger on it and that it will immediately accept a charge where a cold battery at -40F will not accept a charge for several minutes or even hours even if placed in a warm building.

Finally, there have been developments in battery chargers since I penned that article. Now I would recommend a battery minder or maintenance type charger. These use solid state electronics to measure the battery state of charge and will increase the charging rate if the battery is low and then reduce the voltage and current to minimum levels if the battery is fully charged. These provide more accurate control of battery charge and extend battery life just as solid state chargers have done for common rechargeable household batteries.

I hope this answers your questions and I thank you again for defending my articles against comments from "someone on the internet". There is a lot of information out there on the internet and I am constantly amazed at how bad some of it is. I try to base my articles on the best information available at the time, over 35 years of personal experience working professionally on vehicles and on the accumulated 350 years of professional auto mechanical experience of my teaching colleagues. Between the members of this group, we have answered many questions and fixed problems that even the factory technical experts couldn't answer so I am proud to work with them.

Please feel free to post this to the web site forum if you wish. I don't mind being challenged - after all, I am human and make mistakes too, but I wish they would base it on information that is accurate. Then it helps everyone.

Sincerely,
Jim Kerr "

 

Thanks, the poor horse is dead but I think it might be growing feathers :-)

Okay so on 2 Amp mode my/non-trickle charger connected to one RX-8 battery sitting on the shelf delivers 14.5 volts. On 10 Amp mode the charger delivers 15.7 volts but the draw was only about 4 amps. The amount of current drawn is related to the internal resistance of the battery and it's charge. As you increase the voltage delivered at a given resistance the current goes up. Trickle charging implies a small current so I picked 13 volts off the top of my head, that's enough to charge the thing slowly, my 14.5 volts is a bit high because my charger has no premise of being a trickle charger. The answer could be close to 14 but it's all in the same ballpark.

On the net I found an efficiency number for flooded wet batteries which basically relates to internal resistance. The number is typically 26%. What this means is to fully charge the battery from dead to 100% you would need to supply 126% of its rated capacity in watt/hours. Charging the battery is like taking a cup and a quarter of water and dumping it all into a one cup container. You end up with one cup of water to use later and a bunch of water pours out onto the counter. The bunch of water on the counter is equivalent to the waste heat. In the battery the energy is not stored like water in the container but it goes into a chemical reaction, discharge is the reverse. So in actual fact the number that I pulled out of the air for the first calculation grossly unders estimated the charging efficiency of the battery. i.e. I estimated 50% heat generation and it should be around 26%, interestingly a NiCd battery is a lot worse at 40%. The journalist also misunderstood my statement about waste heat. The goal is battery charging with a battery charger the heat is waste, whether you put value on it that's another question, strictly speaking it is waste.

1.5A X 14V = 21W X 26/100 = 5.46W X 3.41 = 18.62 BTUs

It is ends up being worse than I originally though based on the efficiency number.

Here are some efficiency numbers: http://www.windsun.com/Batteries/AgmTech.htm

It is obvious that the battery is filled with lead plates, plastic dividers and maybe pourous sleeves. All of this is immersed in a sulphuric acid solution and when the battery is discharged it is about 90% water by volume. You are not just trying to heat the liquid you are trying to heat that 43lb mass which is a combination of solids immersed in liquid, there are different heat retention properties in play there. From what I can find on the net the average car battery contains about 26Lbs of lead. When you subtract that and maybe five pounds of spacers, sleeves and other internal components you still have a dozen pounds of liquid or something missing from the equation. The heat capacity of water is 4.18 and lead is 0.13 so the lead will heat 32 times more easily. Sulfuric acid is 1.42 but it's percentage of concentration varies with charge from 10% to 60% or something. I would say my first assumption was too high but 3Lbs is too low because there is too much missing weight and some account must be taken for the other materials. At 32 to 1 the lead is equivelent to about a pound of water. Realistically maybe somewhere between 5 and 10 would be reasonable, I will compomise at 5.

18.62 BTUs/5Lbs = 3.72 degrees with no loss.

I only used 12X12X6 as an assumption . . . We can use his precise number of 2.9.
2.9 X .55 U X 40 DTD = 63.8 BTU/hour loss

For comparison I looked at the the insulating values of vinyl siding versus single pane windows and they are very close at slightly less than R1 so the comparison is reasonable. Yes some batteries are shielded, many are not. Of three cars I have, one has flow through ventilation, one is fairly sealed and one is wide open. Even when boxed maybe you can add another R1 for the plastic case, not such a big deal. There are some assumptions about wind in build heat loss calculations, some sheltering will help but we are still losing thee times more heat than we are adding, 18.62 in 63.8 out.

Actually I can't feel a damn thing at -40, really though even charging batteries with a regular charger while mounted in the car when it is freezing cold, none has felt warm to the touch.
This is something I brought up earlier. Continuous trickle charging is actually worse for batteries than intelligent cycling based on battery condition. In power protection systems for computer systems, the trickle chargers kill batteries faster than the smart systems that aren't constantly charging, there is a whole industy built around smart charging batteries. This is a double edged sword in your battery warming scenario. The battery won't be getting charged when it is full so no heat is generated. There is leakage of a few percent per day in lead acid batteries so it will cycle on now and then.

Like two peas in a pod I must say . . . Hey I make mistakes too, some of my assumptions were a bit off but it doesn't change the end result. The end result is kind of obvious to me, kind of a common sense thing. Yes I too wish people would publish information that was accurate.

I can't believe we are still discussing this, we are talking about the heat output of a typical incandescent night light trying to heat a huge honken battery versus old man winter in Winnipeg.

Maybe it is time for an experiment:

1 Extra large black from Tim's.
6" Duct tape
1 Night light
1 Extension cord

Tape the night light to the bottom of the cup, set it outside and plug it in and see if it doesn't freeze fairly quickly at -40 with 10 watts of heat under it. Now be careful and don't spill the coffee, that would be dangerous . . .

Personally I am so convinced that the sucker will freeze that I will just go ahead and drink mine warm :-)

 

hi all, Im in Fort McMurray and if you live in Canada you must know how cold it gets here...I had to park my baby november 2nd..its sitting in a none heated port i built for it...I started it about 3 weeks later no prob...now after weeks of -40 Jan 5th i tried again..needless to say no luck it turn slightly..I boosted it and after about 20 min of trying i was able to start it...It felt gooooooood..I think the car alarm drains the battery as well..I will keep starting it now evry week and letting it run for about 15min until I could drive it...I miss my winter car is only a Celica

 

I came to this thread because I live in sunny San Diego and I left on trip for 7 days and came back and the battery was dead. I jumped it and I was good. A few weeks later I went out of town again...and same thing. I think there must be an amp pull from the battery that drains it. I can't figure it out. I took it to the dealer left it there and came back after work to pick it up...because they told me it was ready. Well, I get there and they had a bunch of wires running from under the hood and from the driver's side door. Bottom line: They were installing an alarm. I asked the guy what was he doing he was like putting in the alarm you ordered. Man, they had my car another full day to uninstall the alarm. When I got it the next day, they told me that everything was fine with the battery. Typical get you out of their face comment.

A couple of weeks after that, I had a 600 watt amp, speakers, and two 10" kickers put in it...awesome, much better than the stock Bose system. Anyway, I did the dreaded pull the car out to wash it and of course flooded it so bad that I couldn't get it to start. Needless to say I drained the battery and jumped it and kept trying for about 20 more minutes...no go. I had it put on a flat bed tow truck and off to the dealer.

Well they got the gas out of the engine, but now tell me that the battery is draining now because of my after market equipment. BS, there is no power going to the amp when the key is off. I told them to pull the fuse at the battery and then test it...they said they wouldn't test it again until I took all the aftermarket stuff out. Don't go to El Cajon Mazda..period. If you live in San Diego go to one of the other Mazda dealers...there service sucks.

Ok, now that I have shared my frustration with all of you, I'll get to my question.

Is anyone else that lives in a warm climate having a problem with their battery dying after a week or so of not driving it???

 

I honestly think not driving it for that period of time will drain your battery because of the alarm needs power to operate.

 

I agree that this may not be a problem, the dealer may need an attitude adjustment though.

- 7 days * 24 hours = 168 hours
- Typical lead acid battery loss through internal leakage 2-3%/day
- Canadian RX8 battery 52 Amp/Hours I beleive (US version is supposedly much smaller)

Conservative natural leakage:
2% * 7days = 14%

Remaining capacity after leakage loss:
52A/H - 14% = 44.72 A/H

Current draw required to kill the battery in a week:

44.72A/H / 168H = 0.266 Amps or 266mA

Let's assume the US battery is only 60% of the size:

60% * 266mA = 160mA

That's not a huge amount of drain when you consider the cars computer, alarm and maybe other controls will constantly be drawing power. You probably lose 10mA to the alarm LED on the dash alone.

It is easy enough to check things. Just pull the negative battery cable, connect an ammeter between the battery terminal (-) and the negative battery cable (+). Set the meter on a scale greater than 200mA DC. My guess is that you would see somewhere around 100-200 mA. If you want to see what is drawing all the power, start pulling fuses one by one, when the current draw drops a lot you will know which circuit is the culprit.

I would see if the battery is physically smaller than ours, if it is I would buy a larger one. All I have seen are posts that the US battery is smaller, I have never seen a spec sheet or anything.

Here are the dimensions of my battery for comparison: 6 5/8"W X 10 1/8"L X 7 7/8"H (casing not terminal height)

 

My US stock battery: 6 5/8" W x 7 3/4" L x 8 3/4" H (includes 3/4" post).

According the the service manual, "back-up current" is supposed to be 20 mA max.

Does your battery fit so that front edge is half way between the white painted area as shown in the following TSB @ the top of page 2? :
http://www.finishlineperformance.com.../01-042-04.htm

 

You'll have to forgive me, but I stopped reading replies about 3/4 of the way in. :D


I just have one question: has anyone checked to see what current their 8 is drawing after their car is shut off and keyed off?

You know the test - disconnect the ground from the battery and put a multimeter in line with it.

I'm not disputing anyone's stories here, but I find it surprising that a battery would be dead like that after sitting in the cold. My own RX-7 has repeatedly sat *outside* for up to a week at a time, including through both cold snaps (-30C) and she fired right up afterwards. (I'm saying that during the cold snaps she wasn't driven for at least two days before and two to three days after.)

Same size rotary engine. Different electronics.

That may not be the same as two or more weeks of being idle, but it still makes me wonder. Especially with the dead batteries happening to garaged cars.

Anyone?

 

From what I can remember there was only about a half an inch of space between the battery and the front of the case. My battery is inside the house right now, that's why it was easy to come up with the measurements. I double checked my length measurement and it was correct so the US battery is 2 & 3/8" shorter and almost certainly would have less capacity.
That seems low, based on a that it would take over three months to drain a CDN battery. Now it takes a lot of juice to start the car but in theory you should easily be able to start it after a month when it would have lost a third of it's charge.
Not me . . . I only ever killed the battery once by accidentally popping the trunk lid. I don't drive it in the winter and in summer I can't drive it enough . . .
I agree that all of this is surprising. My winter car sits unused for several weeks at a time in the summer and I have no trouble starting it after that. My guess is that somewhat more current is being drawn than advertised, I guess I could measure it at some point . . .

 

i say just plug the damn car in

 

My car sat for 3 weeks and wouldnt start/flooded. I followed the flood start proceedure while boosting the car and started it up.
Since then I leave a smart trickle charger (ACI supercharger) on the battery. No starting problems at all. So there does apperar to be some drain.