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 :(

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. ;-(

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.

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.

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.

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.

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.

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.

Through in the towel on the old battery and ended up buying a 51R that 2Rismo suggested.
Cost $120 Canadian at Walmart (thats about $20 USD lol), wayyyy heavier, and dropped right in once I got rid of the tray. Not sure if I really needed that tray.
I read a bunch of threads about having trouble making space for the 51R, but I guess I have more space with my intake in there.
Getting down to -30 on the weekend, so that will be the real test!

https://cimg7.ibsrv.net/gimg/www.fit...2ad1755152.jpg

I kept the tray, just trimmed a couple spots on it,, it keeps acid residue off the metal support.
Option 2 is to use spray bedliner to paint the metal tray before you install the battery.

Dear Kingkelly, are you sure the alternator is charging the battery correctly? It may have a problem, or your electrical wiring may have some bad contact, especially on the body and chassis ground.There may also be a bad contact in positive wiring. I have seen a similar problem in a car that due to bad contact, did not charge the battery properly, it was always half loaded. If the problem is of this type, while the battery is new, the problem will disguise and the system will appear normal. As the battery gets older, the problem will appear again and you will blame the battery again. I advise you to measure the current (Amps) that the alternator is supplying to the battery. This test would be pretty conclusive. Bad electrical contacts drive technicians to madness. They are hard to find and cause severe headaches. Greetings.

Thanks, I did think it was the alternator for a while, as my Fit had trouble starting up once on a hot summer road trip.
I think I will look up how to measure the amps the alternator is outputting. Not sure if its worth replacing the alternator though if that is the cause, would cost a pretty penny and seems too tricky to get to myself. Will save me some grey hairs down the road though!

Dear Kingkelly, I live in a tropical country where 15 degrees Celsius is considered cold and the girls take advantage of their boots, which are kept in the closets for most of the year. In our summer the temperatures rise from 30 or more easily and we have to take several showers a day. You can laugh but it's true. Starting an engine in a -30 degree environment should be much more difficult. The spark plugs must be well cleaned and with the correct gap between the electrodes and the spark also has to be very strong. It is always good to keep these items in good condition because who ends up suffering is the battery and the starter. I am going to measure the battery voltage of my Honda Fit 2017 with several connected consumer power devices and I will give you the voltage value. My car is in perfect condition, so you can measure the voltage on your battery with several consumers and get an idea of ​​the state of the battery charging system. Do you have a digital multimeter?
Engine stopped 10 days ago: 12.46 VDC
Cold engine at idle: 14.44 VDC
Engine running at 2500 RPM, headlights and air conditioning on: 14.30 ---- 14.40 VDC.
You can compare these values ​​with those of your car taking into account that my car is functioning properly.
Greetings and good luck.