Hot Battery

[Petrol Pete]

A few days ago on here a few of us got into a conversation about how an overheated battery can act just like a battery that is very cold (especially if it is an old lead acid type) IE: very slow engine cranking on a hot day.

I myself replaced my original (12 yr old) battery as a precaution when I had a few 'weak crank' issues on hot days. I was a bit puzzled at this as this battery has never let me down despite the car standing outside in freezing temperatures, sometime for weeks on end when I have been away on business trips. I Googled it and saw that an old battery could fail when hot just as quickly as it can when cold.

This is what started the discussion as many of us on here have lived in hotter climes and not really experienced this phenomena much , it was also mentioned that older cars that had the battery in the engine compartment had a lot of 'space' around them (ventilation) where as today engine bays can be very cramped...not many as cramped as a C55 AMG !...mine has a big battery and not enough room get a hand in almost anywhere under the bonnet.

So anyway , I said I would take some under bonnet heat reading on a hot day. Well that hot day well and truly arrived...here are my results.

I used my trusty B&Q special Stanley STHT77365 IR non contact digital temperature gauge ...All 35 quids worth. good enough for this experiment..it will have to be , the £7K+ FLIR unit is locked away at my last place of employment and I am unlikely to be able get my hands on it any time soon.

Outside temp according to Mercedes Benz 28'C (driving)
Park car . let it idle until fan kicks in and out
Bonnet temp (silver) 48'C
Wiper arm pivot temp (black) 46'C
AMG name badge on engine 59'C
Battery temp 50'C

The battery is (as are most that are in the engine compartment these days) is in its own 'sealed' space. I doubt here in the UK that I would be able to see a much higher battery temperature but a quick search on line will show that 50'C is at the very upper end for safe battery temperature. I am not talking about battery temp while on charge but in normal operating environment.

I am not trying to prove or dis prove anything by this it is more to satisfy my curiosity ,but it would indicate that putting the battery in the boot is no bad idea despite the cost.

We have a member on her from Texas who has stated 3 or 4 years is good going from a battery over there , I have no doubt people in the desert states who own older cars have a similar experience.

PS . I would have posted this on the 'Battery' part of our forum...be we don't have one.

 

[markjay]

Having the battery fail on 'hot days' is puzzling.

The normal temperature under the bonnet with a hot engine will almost always be higher than the ambient temperature with the engine cold.

If what you are suggesting is correct, and the battery fails on hot days with the engine cold, then it should also fail in the same way whenever starting an already-hot engine any time of year (apart from in very cold weather)?

Also this would have meant that the majority of cars in Spain, South of France, South of Italy, Greece, etc, will have an issue with starting the engine most days....

I think that whatever temperature-related issues you are experiencing with the battery, are simply due to the battery being on its last leg and needing replacing.

I can't see a healthy battery having any difficulty in starting the engine under any ambient temperature conditions (apart perhaps for very extreme ones).

The temperature (too cold / too hot), does have an effect on battery life, i.e. it will shorten it. But while the battery is still good, the temperature fluctuations should impact on its performance, not to a degree that will cause difficulties in starting the engine anyway.

 

[Petrol Pete]

Markjay, thats what the post is about really, 'older' batteries having just as hard time cranking (a hot engine) when the battery itself is hot as when cranking cold with a cold engine.

Totally counter intuitive to what we see as the 'norm' .

 

[m80]

I'm not aware of the hot battery discussion, but can see why there may be issue.

On cold days a battery voltage is likely to be down some.
It may not be fully charged each use due to extra load of many things in use.
Trying to start a cold engine takes more energy than a warmer one.
The continual and increased demand on the battery can cause the internal plates to heat up more and warp if over heated. As and when they come into contact with each other, even though there is an insulator between each plate it may fail, the batteries capacity is reduced.

Also the coating on plates can crumble and fall to the bottom of the cell reducing the good insulation between plates.

But under most bonnets the engine runs at 85 degrees so the battery, more so on hotter days, will be warmed by that. I couldn't say how much difference between cold and hot days and your test is interesting, as would the comparison when cooler outside.

Also not possible to determine is how much alternator charging had taken place prior to shutdown, but that'd be usual so perhaps not of importance.

The closer the battery to the fuses, and so supply to the starter, the less the volt drop during starting, and heavy alternator recharging. So for me rather than reposition the battery at distance, even with heavy duty cables I think I would prefer to carry a spare battery for the event.

An experience some years ago, the Gr Cherokee under bonnet battery voltage rose to 19 volts in a short time while driving (I have plug in (ciggy lighter) volt meters). I shut the engine down as soon as able. It failed to restart.
My theory is a cell had shorted and reduced load on the alternator, that then charged at the over voltage I witnessed.
The battery now at reduced output couldn't restart the Jeep.
Breakdown recovery home and I was lucky there was no electronics damaged. Another battery and all was well.
I'm open to other theories.

 

[Will]

Is it possible that other factors will be at play here - how are the various connections/terminals from the battery to the engine and starter etc, hot wires will have an effect on current flow etc.

I guess to perform a little more of a scientific test you would have to keep the car somewhere with a relatively stable temperature say 10-20 degrees, warm your battery to 50 degrees or whatever and see how it affects stuff compared to before.

I have a cable to replace on my 911, it connects the starter/alternator etc to the positive terminal in the engine bay (at the back). Battery is in the front. There‘s a separate cable that runs from the battery at the front to the rear of the car (much like with MBs that have the battery in the boot)

Sometimes when it’s quite hot (engine temp not just ambient temp!) it cranks over a bit slower, likewise the charging voltage drops. These cables gets slightly corroded/weak in places I understand, and this weakness shows up when it’s hot - the resistance of wires increases with heat, and it can barely draw enough current for its purpose. The battery is fine - replaced just before I bought the car (and I wouldn’t be surprised if it was changed in error due to this issue!)

Not saying that this is the case with your C55, but it does show temperature can affect more than just the battery

 

[Benzowner]

Problem is with a car, on hot days as we have had recently, where can manufacturers place the battery. My W245 had the battery sat under my feet, inside the car and in this weather would sail past 60C, likewise if the battery is in the boot. Maybe they should install a fan for the battery just to circulate some air to cool the battery a little.

Not on a car, but I boiled a battery on my caravan a few years ago, van was on site connected to main electric and we were out for the day. When we returned there was a strange acidy smell in the van. Realised what it was, disconnected the power to the van, opened the battery locker to find an oval shaped battery that was very hot. No signs the battery was on its way out before hand. We were lucky I think.

 

[Petrol Pete]

I suppose we must also remember Tesla cars have cooling systems for their batteries..... I started the thread as it's a bit of an oddball thing for us in the UK to encounter and as a result is probably a rare ( non existent) occurrence for most ,but worth having a chat about.

 

[grober]

Charging at High and Low Temperatures

Learn how extreme cold and high heat reduce charge acceptance, and the battery must be brought into moderate temperature conditions before charging.

batteryuniversity.com

and

Discharging at High and Low Temperatures

Watch for limitations when using a battery at adverse temperatures and how to overcome the effects

batteryuniversity.com

 

[Tezz]

My battery sits cooking inside car under floor when not getting filled with rain water

I remember my dad having a car with a fan on the battery box operated by a temp switch I think it was an old jag

 

[Ted]

My battery sits cooking inside car under floor when not getting filled with rain water

I remember my dad having a car with a fan on the battery box operated by a temp switch I think it was an old jag

that was the xj12. The xj6 might have had it too.
I’ve never heard of heat specifically affecting a battery, although of course they have their limits.
My first job was in a battery shop. The boss used to come in on the first frosty day of winter rubbing his hands an saying “It’s battery weather”
@m80 ’s post has a lot of useful information, and what is often not appreciated is that the electrolyte has a negative temperature coefficient, and its impedence increases as the temperature decreases.
Another thing not often considered is that as the bettery gets older, the internal impedence increases. This results in an obvious voltage decrease under load, but the opposite happens when charged, and the full charge voltage is reached more quickly (and therefore a corresponding reduction in capacity) than when the battery is new.
A short circuit cell will ‘boil’ when a large load is put on it with an accompanying metallic smell - I think it is ozone.
Finally, back in the day when batteries had pitch to seal them, you could tell an old battery that didn’t have much life left as the negative plates would expand and lift the end with the negative post.

 

[grober]

My battery sits cooking inside car under floor when not getting filled with rain water

I remember my dad having a car with a fan on the battery box operated by a temp switch I think it was an old jag

xj6 battery box