Dead battery, reversed polarity on jump, won't turn over with correct polarity

Question

Total #rookiemove on my part - it was late, dark, I'd shovelled snow for an hour then decided to try and jump my car that had been sitting in the garage for at least a couple months without being started.

This is a 2008 Mazda 3, afaik the battery is 10 years old. I haven't driven the car for a couple months and it wouldn't turn over. I used jumper cables attached as follows, in order:

• Mazda 3: correct polarity directly on battery terminals
• Running car: negative clamp on positive terminal, positive clamp on remote clamping tab

With lots of sparks on the final clamp, I attached the cables for ~5 seconds before I noticed. I didn't attempt to start the Mazda with incorrect polarity. I corrected my mistake and at this point I didn't hear the starter on attempted ignition.

Fortunately the running car has continued to run without issue. I returned and checked every fuse on the Mazda 3, all intact. I don't know how to test the relays. My multimeter read 3.2VDC on the battery. The little security light in the console was still blinking, and the cabin light came on very dim.

At this point should I buy a charger and try to charge the battery? Would it be dangerous to do so indoors (due to possible damage?) Should I replace the battery? Are there any tests that can be run on the battery? Should I verify other components?

Also: how should I maintain my battery if I won't be driving this vehicle often?

Answer 1

For a battery thats 10 years old is very very old..

If you are not starting your car atleast once a week to keep the battery flowing id get a device that does a small trickle of flow to keep battery from just sitting because that really damages the internals.

Can test the battery by taking it to an auto parts store like napa, autozone or o'reilly's.

You most likely need a new one though and for a 10 year old battery in the cold most likely wouldnt start a car very easily if at all.

Check an see if fluids are low if possible before you do all that and make sure its filled to the top then bring it into the house and set it on a piece of cardboard and use a battery charger and let it charge fully, then once full take a volts meter and see if your getting about 12 volts, throw it back in the car and try it once more.

If battery is good id really check all fuse boxes and cables.

Hope this helps you out a little bit.