I read that you should disconnect a car batteries negative cable if not using a car for extended periods as this could lead to electrical devices draining the battery especially in new cars with a lot of electronics.

However apparently you do not need to do this with older cars, perhaps because there are less electronics. Does that mean if I have an old car such as my 1999 civic vti, I can leave the battery connected and not running for 6-12 months then expect that the car will still start up on crank without the battery being drained and a need for a jump start?

I had the impression that most cars including old needed a jump start when not used for a long time.


With older cars, the only likely key-off drain would be the clock, and maybe feed to the radio for maintaining presets, which won't add up to anything significant, but the battery itself has a self-discharge rate, and for a period of several months or more, I'd be either removing the battery and storing where it could be periodically checked and recharged, or connecting a battery tender (monitor + low current charger) if it's left in place, or you'll find the battery fully discharged, and even though it will start and begin to recover with a jump, the battery capacity tends to suffer with deep discharges.

  • Just to see I've understood you. You are saying that after 6-12 months the clock and radio would unlikely cause it to drain, however after 6-12 months the car may not start on crank because the battery may have self discharged and hence there will be a need for a jump start? thanks. Oct 9 '19 at 16:12
  • Yes, Clock and radio drain wouldn't fully discharge a battery over a few months. I wouldn't leave a battery unmonitored for more than that, even if disconnected. If it's a new battery it may survive, but older batteries tend to worsen their self-discharge characteristics, probably because of contamination of the electrolyte. My lawn tractor, motorcycles and vehicles not used during winter all have their batteries in the basement during winter. I can then check them every month or so, and charge them if needed.
    – Phil G
    Oct 9 '19 at 16:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.