What will drain your car battery? | AutoGuru
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Top things that will drain your car battery

Lindsay Saunders

Updated 6 May 2021

Lindsay Saunders

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You jump in, push the Start button and . . . nothing. Nada. Zip.

It’s never a great feeling and while there are ways to get yourself going again, let’s take a look at the top reasons your car battery can go flat.


Top of the list, and perhaps one of the less obvious reason, is the alternator.

A faulty alternator can prevent your vehicle from sufficiently charging the battery enough to start the car again and can even fail to produce enough electricity to keep the vehicle running.

Ever noticed the headlights or interior light gets brighten when you rev the engine?

That’s your alternator not living up to its job description and you need professional help before you get stuck.

You can check to see if you have an issue with the alternator by starting the vehicle, then disconnecting the positive terminal of the battery.

A properly functioning alternator will produce enough electricity to keep the vehicle running without the battery, but if the vehicle shuts off, the alternator likely needs to be replaced.

Loose or stretched belts and worn tensioners can prevent an alternator from working.

Here's some more drainers:

  • Headlights or interior lights left on​​​ – they can drain a battery dead, even that itty bitty interior light. Some vehicles’ headlights and interior lights fade off after you lock the door – just keep an eye on them to make sure they do.
  • Battery in weak or poor condition – A poorly maintained or weak battery nearing the end of its life may not hold a charge well and even small drains, such as the memory function in the car’s sound system, could kill a weak battery. Ensure you have your battery checked and maintained at each service.
  • Corroded or loose battery connections – These prevent the charging system from topping off your battery when you are driving. Again, maintenance is the key.
  • Other parasitic drains in the electrical system – these can be difficult to find, but they are capable of killing batteries dead. Common drains include glove box and boot lights that come on or remain on, when they shouldn't.
  • Extreme temperatures – Hot or cold weather won't kill a battery that's new or in good shape, but a weak or old battery may fail in extreme conditions. Exceptionally hot or cold weather can also amplify other underlying issues.
  • Too many accessories – Got your phone, GPS, dash cam and the kid’s DVD players and screens all plugged in? Make sure the vehicle is shut off completely or, if you are going to be sitting in the one place a while, idle the engine. All that tech can run your battery down.

Like so much to do with our vehicles, maintenance and a little bit of attention can prevent most of these problems occurring.

But if you’ve a battery or electrical issue, it’s always best to talk to an expert.

That’s where we come in - next time you need a service, repair or inspection, visit AutoGuru.

We let you search and book from thousands of qualified mechanics, who eat car troubles for breakfast.

Lindsay Saunders

Written By

Lindsay Saunders

Lindsay Saunders has been writing, editing and producing words and photos for more than three decades, starting back when he drove a 1971 VW Type 3 fastback.

Now he’s got a Hyundai I30 diesel, a 1999 LWB Hi-Ace (camper project) and wishes his wife’s EJ Holden station wagon was actually his.