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Why does my car battery keep draining?

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Updated 6 Sep 2021

Jason Unrau

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Turn the key in the ignition and the engine fires up.

At least, that’s what’s supposed to happen.

But if you hop in the driver’s seat and turning the key doesn’t result in the satisfying crank-over and exhaust rumble, it could be a common problem – a flat battery.

While it’s a car issue many drivers have faced before, it’s also one of the most frustrating.

It takes time to jump-start or recharge the battery every time.

And if it happens frequently, you lose all faith in your car’s reliability.

What might be causing your car battery keep draining?

Learn more about the three main causes for a frequently drained battery.

Internal battery fault

The average lifespan for a car battery is between three and five years.

Anything more can be considered as borrowed time.

As a battery ages and after thousands of driving cycles, the battery simply doesn’t recharge to its former full capacity anymore.

Extreme temperatures can accelerate the condition, and every time the battery is completely discharged, its capacity is diminished.

A flat battery can often be attributed to it being old. While the battery might be faulty and need to be replaced, a bad battery can also be caused by other symptoms as well.

Charging system failure

A car’s primary component to replenish the battery’s charge, as well as to maintain the electrical system’s operation, is the alternator.

The alternator generates an electrical field and the energy is stored in the car battery.

The car’s electrical system operates mostly on the alternator’s juice as well.

If the alternator isn’t working as it should, whether due to part failure or another electrical or wiring problem, the battery won’t be recharged while the engine is running.

Once the battery is depleted, either partially or completely, the engine won’t start.

Parasitic load

Today’s vehicles are chock full of electrical components and modules, all of which require electricity to operate.

If the engine isn’t running, they draw power from the battery’s stores.

Occasionally, a module may not turn off when it should, an electrical part might erroneously demand power, or an electrical short can sap off the battery.

It’s called a parasitic load – like a tick sucking the lifeblood from the electrical system.

Parasitic loads can be difficult to trace.

Most of the time, the electrical draw seems minimal and might only drain the battery overnight or even over a few days.

Nevertheless, a parasitic load has the potential to leave you stranded.

How to deal with a battery that keeps draining

If it’s a one-time deal that you have a dead battery, simply boost it to use it and recharged it fully as soon as you are able.

If it keeps going flat on you, there’s only one correction: have it properly diagnosed by a professional mechanic.

A mechanic with experience in electrical systems will perform a load test on the battery and charging system, check the alternator’s output, and test for parasitic loads.

Anything less is just throwing darts at the problem.

Are you looking to get your battery problem fixed?

Find a high-quality, local battery specialist through AutoGuru to get it inspected.

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Written By

Jason Unrau

Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.

One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.

Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.