How to store an unused auto battery


I’ve had a 12 volt car battery that I don’t need right now.
What is the best way to preserve it for future use?


Out of freezing, with a smart charger on it.

How future ?
Maybe just sell it and buy new when needed.

Fully charged and in your basement, what I do. Maintains its full charge over the winter anyway.

They say that leaving a bare battery on the concrete floor draining a battery is bunk, never made much sense to me.

IIRC that was true decades ago. The newer cases post WW2 (?)
didn’t do that.

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Let me see if I understand. You recommend storing it in a environment above freezing and attached to a smart charger.



I guess I should ask: lead-acid, or AGM? How long will the battery be stored?

As for the old story of it leaking electricity onto concrete? That went out with tar-case batteries.

Stick in a well-ventilated space, with the smart charger on it, and Bob’s yer uncle!


I don’t know if it’s lead acid or AGM but will check tomorrow.

And, short of connecting it to a vehicle and cranking, is there any way to determine its condition?



A battery hydrometer will indicate the level of charge (if cells are accessible) but it won’t reveal high internal resistance.

A battery load tester is similar to testing it on a car. It’s a voltmeter together with a load resistor that you use for a very short time so that the resistor doesn’t melt.


Most repair shops should have a battery tester that they will be able to test the battery, do that then you can proceed with the best option for you, sell or place on a CTEK battery maintainer.

The battery in my daily driver 2000 S-Type went dead a few months ago, and after replacing it, I put a low-priced trickle charger on it. Success, it was back in charge a month later and starting another car.

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I’m with Jerry. Sell it, cheap. Buy another, if and when needed.

But, other comments are valid. charge as needed. Slow is best.

I have an old one on my bench. Durn post “melted”. A weakness of side post batteries. I sed it for a time as a bench battery. I am reasonably sure it is 'dead". Just for the heck of it, I might put my smart charger on it…


Agree with a trickle charger / smart charger. Best to charge it fully first with a regular charger if possible. I have my XJS battery off to the side in storage this way. I use it here and there while working out electrical issues during the XJS’s refurbishment or testing items on the bench. If I don’t drive my XJ6 for more then a week or so, I throw one on it as well. Never had an issue, and the XJS battery is going strong for over a year or two. If you won’t need it for a few years, better to just sell it if possible.