Why do batteries fail more in winter?

Batteries work by a chemical reaction, these reactions work better at higher temperatures. full details of everything you could want to know:

As batteries get older, they lose capacity, or get weaker. During warmer weather the engine is relatively easy for the starter motor to turn over, so even a weaker battery can still start the car. At low temperatures all batteries, even newer ones, deliver less power. At the same time engines become stiffer to turn. A good battery has enough reserve of power, or current to cope, but the combination of a weaker battery and a stiffer engine, can mean an older battery just can't deliver the extra current needed to start, even if it can turn the engine over. That can take virtually all the current the battery is able to deliver, leaving too little for the plugs to spark. A simplistic explanation, rather than a technical one. Mike.

Not forgetting that the load on the car from more headlamp, wipers heaters etc add to the load on the alternator and battery, my MK4 Golf required a new battery after 3yrs,I don't expect the MK5 battery to last as long due to more powerconsuming equipment on the car especially the auto lights feature...

You may be in for a surprise. Batteries tend to last better than ever these days and eight years is not uncommon. I have recently changed the original battery on one very electocentric vehicle that I bought new in early 1993. Another lasted from '95 to '03 and another vehicle has lasted from '98 to today so far with no sign of deterioration. It is VERY unusual for a quality battery to fail at three years and many have a warranty that covers for that long.

Huw

because they are cold bloodied? or perhaps they don't go to the library to do their homework? ::)

Absorbed Glass Mat batteries can easily do 10 years provided they're not run flat (which permanently damages any battery). Mazda MX-5's have them.

They don't fail more in winter - they actually "fail" more in summer. It's only winter that brings out the problem.

Heat is what kills batteries over a period of time - it reduces capacity, cranking current, etc due to deterioration of the plates.

When winter comes, the problems are apparant. The engine oil is thicker, meaning more resistance to turning the engine. When a battery is cold it can deliver less power as well. The two effects - more power needed and less able to deliver that power shows up the deficiencis in the battery that was caused by the hot summers.

AGM batteries are good for a long period as well if you don't flatten them, which can make them unchargeable. Decent flooded wet batteries, provided you keep on top of them with distilled water can go for a long time as well, I've had seven and six years out of flooded batteries with no real problems - in both these cases the batteries passed on with the car and ran for a while after that.

Problems seem to start around year 4 with a drop in CCA, (shown on a heavy discharge test) but as long as the battery can deliver the cranking current needed for 15s and then bound back up to 12.2V within a minute (this is an easy home test) then it's almost certainly good enough for another winter IME.

My Dads 1993 Audi 80 is still on it's original factory fitted battery. Used daily and still spinning over strong.

But all this 'load' comes from the alternator - not battery.

I suppose in fairness even though the car was just under 3yrs old FVWSH the stealership had not completed all the checks cos the battery fluid was well low in many of the slots (overlooked at the services?).

I think you've just been unfortunate. I don't think the running load on a battery affect it's life. I would expect one to last at least 5 years regardless of the demands made on it in normal use. That is providing the charging circuit is kept in good condition. I usually buy cheaper batteries. Around £40 for a 70ah. Even so, I've never had less than 5 years out of any of them. I would guess about 5.5 years is their average life. Mike.

The lights remain on after the engine is switched off for a couple of minutes (dipped beam) and also when approaching the car when the ambient light is below a certain level.

Just pulling a set of cells out of some ex-BR equipment, the tags read at least 18 years old, three times their operational lifespan and they are just starting to calcine inside.

The message from "Avanti" contains these words:

You can probably get the dealer to change the programming for that.

Our summers aren't normally that hot.

No, but sat in a traffic jam in a warm summer sucking warm air through the radiator with fans and dumping it in the engine bay can produce very adverse conditions. I think this is one reason that many makers have started relocating batteries to places like under the rear seats, now that AGM and non venting batteries are becoming cheaper.

And a couple of minutes at 10 amps load isn't going to seriously upset a

Total lighting load is likely to be