I need a new battery for my Land Rover, but I’m confused by the ratings – amp hour, cold cranking amps and reserve capacity. What’s it all about? And how do I choose the best one?
Phil Watson, Manchester
Yes, it is confusing. The amp hour is how much current it will supply continuously over a fixed time – usually 10 hours, but it can be five or 20 hours, so unless you know the times used it’s not possible to compare batteries. Cold cranking amps is how much current is needed to run it down to 6v at -18ºC, but some batteries are marine rated, which is at 0ºC – so the fi gure looks better. Reserve capacity is the only one that’s easy – it’s how long it will supply 25A before it drops to 10.8v; for a Land Rover battery that’s usually 60-90min.
Which to choose?
I just recommend buying the heaviest lump of lead you can get for your money. Battery technology hasn’t advanced much since the 1980s, which saw the replacement of antimony with calcium. Try not to buy a cheap sealed battery, you can’t top one up!
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