Car battery

[JohnD]

yes, we have.

Small, light, lithium batts.

 

[ban-all-sheds]

Yes, and when jump-started, half a mile and it will start on its own and then rest of the day normal driving, it's ok.

I know that's what they do but am trying to understand why.

I can understand that they wear out and get 'weaker', as I called it (after all eight AA batteries are 12V but they won't start a car) but what happens in the first five minutes to make it alright again (temporarily) but leaving it overnight is back to square one (constant drain aside).

I would have asked if you notice this behaviour in warm weather, but presumably you aren't experiencing bitterly cold nights.

Johnny Foreigner battery - by 31/3/17 Empress Treeza will have set in motion the process which will mean that you either have to stop buying them or become a Johnny Foreigner yourself, and then we can all spit on you and your flaky battery.

 

[ban-all-sheds]

yes, we have.

Small, light, lithium batts.

Which combustion-engined cars offer them as standard, or even an option, in place of a lead-acid one?

 

[JohnD]

I don't know.

 

[ban-all-sheds]

I think you probably do.

 

[securespark]

Yes. There are more modern technologies, but they are based around lead/ acid: AGM and ECM: Absorbent Glass Mat and Enhanced Cycling Mat.

There are also "calcium" batteries; "Silver Calcium alloy batteries are a type of lead-acid battery with grids made from lead-calcium-silver alloy, instead of the traditional lead-antimony alloy or newer lead-calcium alloy. They stand out for its resistance to corrosion and the destructive effects of high temperatures."

 

[ban-all-sheds]

There are all sorts of battery technologies. I'd be surprised that if money was not a consideration that there was nothing better for this application than the sort invented over 150 years ago.

 

[JohnW2]

.... if a chap were to go out and spend, literally literally, £millions on a brand new car, why would he be stuck with the same 150-year old battery technology as the chap who buys a Dacia?

Are you sure he is?

I know that lead-acid batteries are good at handling short duration monstrous loads, but even so, have we really not managed to design anything better in the last 158 years?

I would have thought so, too, but I don't think (m)any of the newer technologies that are in widespread use can cope as well with those brief but monstrous loads as can the lead-acid one - and don't forget that (other than the 50mA or 150mA mentioned by EFLI), in contrast with the past the batteries do not have to do anything other than start the engine, so there has perhaps been very little incentive to bring new (and probably expensive) battery technology into cars. Are you old enough to remember the days when long car journey's at night were problematic in some cars, if the dynamo could not keep up with the headlights etc., leaving one was reliant on a progressively discharging battery?

Kind Regards, John

 

[ban-all-sheds]

I am just about old enough. And even if not I remember a car in which I installed over 800W of front lights. Although to be fair I never used all of it for long enough to drain the battery.

 

[WhydidIstart]

I know this thread is a week or so old, but on the subject of the car starting ok after being jump started but not starting the next morning, the current required by the starter to start the engine is likely to be much higher the next morning when then engine has had time to completely cool (plus the extra discharge/ self discharge, etc). If you are using the car in the day, the engine is likely to still be warm the next time you start it and hence much easier to turn over. This is because the oil cools and becomes thicker when cold. The battery itself will also perform better when warm.


Regarding the 150mA current draw, assuming no glove box or boot lamps stuck on as has already been mentioned, aftermarket alarms, radios, amplifiers, dash cams, sat navs, etc are usually the culprit – do you have any of those things fitted?


150mA is also not necessarily out of the normal, many newer large cars like Jan XF, Range Rovers, etc can have high quiescent current draws due to the amount of kit fitted – but these vehicles will typically also have big batteries fitted so they will still start after several weeks of non-use. Some of the Merc models have 2 batteries fitted to help with this situation and make sure settings aren’t lost when 1 battery is changed.

 

[JohnW2]

150mA is also not necessarily out of the normal, many newer large cars like Jan XF, Range Rovers, etc can have high quiescent current draws due to the amount of kit fitted – but these vehicles will typically also have big batteries fitted so they will still start after several weeks of non-use.

I'm obviously not sure what you mean by 'several weeks', but 150mA 24/7 equates to about 25 Ah per week - so (in an ideal world) to become totally flat in, say, 8 weeks would be 200 Ah. If you wanted, say, 20% of charge to remain after the 'several weeks' to start the car then (again, in an ideal world), 8 weeks would need a battery of about 250 Ah - so a very hefty battery would presumably be required (particularly in our 'non-ideal' world)?

Kind Regards, John

 

[WhydidIstart]

I agree with your calculations and I think as you're suggesting a 250 Ah battery would be very large - that's bigger than some HGVs. A circa 100 Ah battery is more typical for the vehicles I mentioned giving just over 3 weeks' standby allowing ~25% remaining capacity. However these vehicles are smart, so as time goes on they will shut down certain systems such as their infotainment which are effectively computers on standby (so you can listen to the radio without the computer having to boot). Other things like keyless entry might slow the car's scan rate and range for the key transponder, etc. So the cars then reduce their current draw to extend the time they can be left unused for.

PS on the subject of newer battery tech see

and

but then also see this from about 2.50 for an idea of why this newer tech isn't that common yet!

 

[JohnW2]

I agree with your calculations and I think as you're suggesting a 250 Ah battery would be very large - that's bigger than some HGVs.

Quite.

A circa 100 Ah battery is more typical for the vehicles I mentioned giving just over 3 weeks' standby allowing ~25% remaining capacity.

As I said, I had no really idea what you meant by "several" weeks - I just guessed at 8 for illustration purposes!

However these vehicles are smart, so as time goes on they will shut down certain systems such as ...

Fair enough - that sounds sensible. However, there seem to be very many cars out there which are not that 'smart'!

Kind Regards, John

 

[ban-all-sheds]

I know that 10-years ago (ish - I'm becoming a bit like those reputed Amazonian tribespeople whose numbers go "1.. 2.. many.." with my classification of how long ago things were) there was a rash of stories of people leaving upmarket cars with newly acquired levels of sophisticated gizmos but no concomitant levels of sophisticated management in airport car parks for just 2 weeks and coming back to find they had a 1.5 tonne hollow steel brick....

 

[ban-all-sheds]

A circa 100 Ah battery is more typical for the vehicles I mentioned giving just over 3 weeks' standby allowing ~25% remaining capacity.

And how long when the battery is, say, 10 years old?