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What voltage is considered a dead battery?

Old 01-13-2019, 12:04 PM
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Question What voltage is considered a dead battery?

My 07 Fit has some troubles starting in the cold up here in the frosty north, and not sure if i should get a new battery or just a battery blanket to plug in.

The battery reads 11.97 volts with just the headlights on
Gets down to 10 volts when its cranking to start up.
Idles around 14.45 volts once its fired up.

Batterys only 2 yrs old, but not from honda
Old 01-13-2019, 04:06 PM
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Testing voltages tells only part of the story; you could line up eight AA batteries in series and get a strong 12 Volts, but they'd be hopelessly outmatched trying to start a car. You also need to test amperage at start and that's best left to an auto parts store to test. If you drive it to the store, most all will test free of charge.

Just for the heck of it, you can also pop the caps off the top of the battery If you feel comfortable doing it. Wear safety glasses, don't smoke. Disconnect the negative cable. You'll likely see tabs where you can insert a screwdriver and wiggle the cap(s) up and off. Be sure you don't short the poles together or the [+] pole to the body with the screwdriver. Check to see if the water/acid level is covering the plates inside and if so, leave it be. If not, add distilled water, but not too much.

Good luck with your work. I agree that your battery should last much longer than two years. ;-(
Old 01-13-2019, 04:23 PM
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Under 12v is usally a sign of a weak/dead battery, but you mentioned that it was with headlights on. Confirm with the headlights off (no load)and see what the actual voltage output is of the battery. If your still under 12.6v then I'd probably replace before you get stranded.

Your alternator output is within the normal range 14.45v when running.
Old 01-13-2019, 04:26 PM
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Thanks for the detailed explanations. I've done the distilled water top up with smaller motorcycle batteries, so i might try that.
Otherwise, probably just go to the dealer and get a proper battery this time.
Old 01-14-2019, 09:30 AM
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If you get a new battery, night as well get a 51r. It has way more cca than the stock battery so would help with starting in the cold.
Old 01-14-2019, 10:20 AM
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Originally Posted by ieandro View Post
Under 12v is usally a sign of a weak/dead battery,
Less than 12.5 VDC overnight, before starting, is considered weak.

Good, complete advice from Alco RS-1. Bear in mind that if you jump-start the car and the auto parts store tests it immediately after you drive it down there, it still might pass...but not provide enough CCA (cold cranking amps) to get your engine running on a cold morning.

Old 01-14-2019, 08:32 PM
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10.5VDC is concidered a completely dead battery, beyond saving. 11.97 is def weak. If not charged back up in a short amount of time, the battery will get too sulfated where it wont hold a charge anymore.
Old Yesterday, 01:36 AM
Join Date: Nov 2010
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Actually, eight AA batteries in series is pretty much the battery that comes with the Fit.

We can complain all we want but it's still pretty amazing that the tiny little Fit battery lasts five or six years under normal circumstances.
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