My azu (602) has a 50 ah battery ,which seems a bit large but then it did have a cb and radio etc before i took it all out, anyway ,it's starting to deteriorate i think and i have a spare battery of the same physical size but 60 ah , so the question is what is standard , and what if any problems will a 60 ah battery cause ,such as will it make the alternator suffer trying to charge it ?

It'll start much better to begin with, but the 2CV charge system will only return to the battery what it can, so better starting won't last.

It'll start just as well, and it'll charge to full.

It's just that both will go on for longer.

If you've got a totally flat 45Ah battery and a totally flat 60Ah battery, both being charged by 25A alternators, they'll both charge to full - but the 45Ah will take (45/25=1.8)hrs to fully charge, whilst the 60Ah battery will take 2.4hrs.

If you leave something on, consuming 10A, then the 45Ah battery will feed it for 4.5hrs until it's totally flat, the 60Ah battery for 6hrs.

(That's simplifying, of course, and ignoring the voltage drop as the battery discharges)

Think of the battery as a storage tank, the alternator as the tap feeding it, and the load (starter motor, whatever) as another tap emptying water out. All you're changing by moving from a 45Ah to a 60Ah battery is the size of the tank.

Cheers good analogy there
Having had a second look the 60 ah one is actually slightly bigger and will over-hang a bit so i think i'll just buy another 50 ah one the right size.

As Adrian has already mentioned, the capacity of a battery in amp-hours (AH) isn't really a guide to how easily a particular battery will spin an engine.

For that, I think you'd need to look at its CCA or CA rating...
< http://www.batterystuff.com/tutorial_battery.html#4 >

ken.

Although, given how small a 2cv starter & engine are, I'd expect anything but the weediest of small-motorbike batteries to cope quite happily. It's not as if it's a chuffin' gurt big diesel 4x4 or truck...

(C)CA = (Cold) Cranking Amps = How many amps the battery can deliver at once. Going back to that water tank analogy, how big the outlet hole is. The starter will only "take" as much as it "needs".

Yeh cranking amps-the slightly bigger one is 550 and the one on the van is 370 , i suppose thats the cca ratings.
The 550 one was off a zx diesel ,but is only physically a few mm bigger which is why by eye i though i might be able to fit it.

Nice explanation, toomany.

Anyways, my neighb bought an immaculate Rover 25 (I know, I know...) a few months ago but didn't use it very often. After 3 weeks of non-use, he found the battery completely flat when he next came to start it.

Off with the battery, into his gloomy garage, clipped on t'charger, set it going overnight. Following day, he replaced the fully-charged battery in his car. Sparks flew as he tried to connect the second terminal, but he told himself this was just the radio or summat drawing a *cough* 'little' power, so he pressed the terminal home...

Wildly fluttering wiper blades, flashing indicators, and god knows what else ensued.

Damage? Well his garage stopped counting at £1k for the engine ECU, £300 for the ABS unit, shagged radio, knackered rear door lock...

The cause? Clue - '...gloomy...'

A thousand quid for an engine ECU? You can go to Comet/Curry/PCWorld and pick up an all singing, all dancing computer that will go online and let you play games and movies and music, for less than half that. These car companies are right proper criminal.

http://cgi.ebay.co.uk/Varta-Citreon-2CV ... 5191a75dd4

Bit OTT for the job and price wise or?