Car Battery - The bigger the better?

[Trevelyan]

About five weeks ago I bought a new battery for my daily hack Vectra, which then got written off last week. I'm toying with the idea of swapping the new battery with the four year old one from my mum's Astra before my old car goes for scrap/salvage. Providing the Vectra battery physically fits the battery tray in the Astra I can't see any real problems in doing this. From memory the new battery was 70Ah, the Astra is 55Ah but I don't think this has any negative effect. Am I right or am I missing something which makes this a bad idea?

[MJK 24]

There's no downside as long as it will physically fit the battery tray and can be secured properly with the clamp.

My Mk2 Scirocco 1600 diesel has a battery from a Mercedes 190 2.5 diesel. Much bigger. It's been on there for years and has never failed to start the car immediately. Even in temps as low as -17 last winter.

I believe they last longer as they're under far less stress.

[Twincharged]

MJK 24 said:

There's no downside as long as it will physically fit the battery tray and can be secured properly with the clamp.

My Mk2 Scirocco 1600 diesel has a battery from a Mercedes 190 2.5 diesel. Much bigger. It's been on there for years and has never failed to start the car immediately. Even in temps as low as -17 last winter.

I believe they last longer as they're under far less stress.

The Ah rating refers to the capacity (i.e. how much charge the battery can store) and there is also a CCA rating (cold cranking amps). The higher the cold cranking amps the more "kick" the battery has effectively. A bigger battery is likely to have higher ratings in both of these areas, and I suppose if its total capacity deteriorates over time it will still have a decent capacity left.

[Trevelyan]

I thought I'd be ok with a larger battery but just wanted to be sure. I'll only get one chance to visit my car at the storage yard and swap bateries so didn't want to take any chances!