Using underpowered battery

James_N

The battery in our car has died, and, because another older car came to an early end a couple of years ago I have a new unused battery - it was bought for the old car in the expectation of another few years, and the untimely end to the older car surprised me. I should have, but didn't, try and get a refund on the new battery (Halfords), and the thing has been stored dry and secure and charged ever since. It's never been in a car.

The battery on the current car has well and truly died, recharging won't hold and the only start now is via a battery pack jumper.

So the old battery (maker fitted) is 520 CCA and the stored "new" one is 470. For this car - 2.4 L turbo, places like Euro carports sell up to about 700CCA for the power requirements, from the cheaper 500 ish level. The 470 battery fits physically and leads all attach well. It secures on the cradle like the original - and it starts the car OK.

Is there any danger, apart from less durability and reliability, in continuing to use the underpowered battery?

chrisw

Definitely no danger. In fact 470 isn't that far off 520 anyway.

AdrianC

No, it'll be fine.

520CCA means it can deliver 520A from cold to the starter motor - cold cranking amps. 470 to 520 is hardly a huge difference, and it's very unlikely the starter will pull more than a couple of hundred.

The other figure you'll find on there is an Ah rating - Amp/hours - the "size of the tank". If that's lower, then it'll go flat a bit quicker.

gilbert_and_sullivan

If it's doing the job on these cold mornings, pray carry on.

Strider590

It'll just fail sooner.

Lead acid batteries deteriorate at anything less than 100% charge, the lower the charge level the faster they deteriorate. So if you use a smaller capacity battery, it'll work, but it'll use more of it's capacity to get you started, meaning faster deterioration. Even though it'll recharge just as quickly from the alternator, it will still have spent time at a lower level of charge than a bigger battery would have.

Joe_Horner

Should be absolutely fine. If your car starts easily then you probably won't even notice any loss of life.

Say your car starts reliably with 5 seconds of cranking, with an average starter draw of 200 amps. That means you'll use (200*5)/3600 = 0.28 amp hours of charge each time you start.

Even small car batteries are rated at 35 amp hours or more, so you're discharging it by less than 1%., around the same as you'd lose just by letting it stand for a week. Not only that, if your alternator has 10 amps available to recharge the battery once it's started, it will take 0.28/10 hours = 1 minute 41 seconds to replace that charge.

Note that those figures are only approximate because of various complicating factors, such as battery capacities varying depending on the size of current drawn, but they give a good ballpark.

James_N

thanks to all posters for their advice

27col

Well, you live and learn. I've known about battery amp/hours, but I must confess that I had never come across the term CCA.