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Battery Ratings


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  • 1 year later...

The two ratings to be concerned with are Ah (Amp-hour) and CCA (Cold cranking amps). These relate to how the battery empties its charge.

CCA is pretty simple, if your battery is 800 CCA, this means it will supply 800 Amps for 30 seconds at 0 degrees fahrenheit. This is related to starting your car and the large current the starter motor draws.

Ah is a little more complicated. It relates to how your battery discharges with a small load over a long time. Amps x time in hours to work it out. Say your battery can supply 4 amps for 10 hours, 4 x 10 = 40 Ah.

When changing your battery, especially on modern cars, it's important to change it for one with an equal or greater rating. With modern cars, if the battery isn't supplying enough power, it can trigger undervoltage faults in components which it turn can trigger all sorts of seemingly random faults. 

I've recently worked on a fairly new BMW where one garage told the customer that they needed a new gearbox because of all the fault codes that were appearing. A quick check on some live diagnostic data with the vehicle running raised my suspicions that the battery might be faulty. On inspection, the battery appeared to be brand new. I spoke to the customer who informed me that he had fitted a new battery a month ago. I checked and the battery he fitted was of too low a rating. Correctly rated battery ordered and fitted and the gearbox came good again. One happy customer with his bill a lot smaller than it could have been.

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