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Should I trust my mechanic and replace my battery now?

I trust the mechanic who told me that my battery was only cranking 295 amps out of the 590 it should be. My battery was original equipment in a 2005 Ford Escape V6, so it's around 8-9 years old. I live in balmy British Columbia's Lower Mainland. My car cranks over strong on the first or second turn every time. I drive only about 3,000 miles (4,800 km) a year and sometimes the car sits idle for a week or more. No problems so far. My inclination is to wait until there's some clinical indication other than the calendar before putting in a new battery. What do you think?

– Bob Friedland, Richmond, B.C.

The signs that you need a new battery are tough to miss – you'll have trouble starting your Escape, or it won't start at all, one expert says.

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"Waiting longer is fine, as long as he's willing to take the chance that he could be out at the grocery store and his car won't start," says Calvin Feist, automotive instructor at the Northern Alberta Institute of Technology in Edmonton. "But if the cranking amps are that low, I'm surprised he's not having problems starting it now."

Your battery's main job is to start the car, and your mechanic says your battery's ability to do that is down to half.

Cranking Amps (CA) determine whether your battery has enough power to rotate the crankshaft – in other words, crank the engine – and activate the ignition until the engine starts. Your battery needs more power to start when it's cold outside, and your battery's ability to start your car in cold weather (which isn't usually a problem in Richmond) is measured in Cold Cranking Amps (CCA).

If the tests are right, your battery should already be struggling to start your vehicle, he says.

Batteries don't have a best before date, but they generally last 5 to 7 years in vehicles that are driven regularly, Feist says.

"I've seen them last that long or longer – but usually in vehicles doing at least 30 to 40 km a week of highway driving," he says.

A battery's life can vary depending on how often you drive and how long you drive for. How do you know if yours needs changing? Get it tested during regular maintenance.

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"Batteries have to be tested to see how much life is left," Feist says.

Feist is surprised your battery has lasted as long as it has since your Escape spends so much time parked.

Starting the car takes a huge jolt of power. The alternator is supposed to restore that power and recharge the battery as you drive.

If a vehicle, like yours, is rarely used and is only taken on short trips, the battery never has a chance to recover the juice it takes to start the engine.

Accessories and computers can drain the battery further while the vehicle is parked.

If that charge is never fully restored, the sulphuric acid in the battery will settle into two layers – with water on top and acid on the bottom. The lead plates inside the battery will corrode faster than they should and the battery will die.

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One way to extend the life of a battery in a vehicle that's often parked is to install a smart charger and keep it plugged in.

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