car battery size?

Mark> There's not a huge difference in price between the different Mark> size amps so I'm wondering if bigger is better. Unless it's Mark> a pricing error, what I don't understand is that the biggest Mark> 88 amp battery @ £39.50+vat is cheaper than the 72 amp Mark> (£43.50) and the 85 amp (£49.00) batteries!!

Battery performnce is rated both in terms of Ah and CCA. Ah (Amp-Hours) is what I think you're talking about, as 88 amps won't start most cars, you usually need a few hundred.

CCA, or Cold Cranking Amps, is the current that can be delivered for 1 minute at -18 degrees centigrade. This is the really important bit that needs to match your car.

Otherwise, as long as it fits and is secured properly (are the fittings strong enough for a bigger battery), I don't see a problem.

Don't try to put in a battery designed for domestic use in a caravan or boat, though. These are often designed for lower current draw but to be discharged more deeply. This could explain the price difference you mentioned above.

Depending on the car a good way of getting extra capacity might be to get the battery for the diesel variant. I can't imagine the battery space is much different to keep the component cost down, and it should be rated at a higher CCA.

AndyC

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A genuine deep discharge battery will cost far more than a car one.

The right battery for your car is important - height, width, depth to fit the battery tray and allow the bonnet to close, right shape of battery post to fit your cables etc.

If you want a more powerful battery, most places list a normal and a heavy-duty version - go for the latter.

I replaced the battery on my car the other day, the replacement was smaller than the old one. But somehow it was rated more powerful. I reckon 'adequate' is about right. After all a smaller battery weighs a whole lot less.

most places I

biggest

I've got a

amp to a 88

different size

pricing error,

£39.50+vat

batteries!!

replacement was smaller

Power and capacity are not necessarily related. A small battery may be made with a high power output, yet low capacity in amp/hrs, as the maximum useable power output depends more on the batteries internal resistance than it's size.

OTOH, a battery having similar power, but greater capacity, usually means making it larger to accomodate more and heavier plates per cell.

11 plates as opposed to the usual 9. Most batteries have enough power for the average car. Personally I prefer to buy greater capacity batteries, with enough power for very cold starts, are reasonably priced, have 3yr guarantees, and can be topped up. I go out of my way to avoid so-called 'maintenance free' batteries. Mike.