Battery had been left no start for months until I found it at 0.45 or so.

Used a charger after an entire day it got to 2.95 volts.

Then connected jump cables to the isolated battery and revved it bringing it to 11.66 volts in 8 minutes.

Left isolated battery in boot and it’s down to 10.5 volts. Can’t be a parasitic drain because it isn’t connected. Would have got colder I’m thisd two hours but I don’t think that causes voltage loss.

So what does all of this tell you about the battery, why did it lose more than a volt in 2 hours even though not connected?


  • If you only got to 11.66V while it was still being charged, it isn't holding any charge at all. That is consistent with 10.5V when it is not being charged. You could try putting it back on your battery charger for another 24 hours to see if you get lucky, before you scrap it. – alephzero Sep 25 '20 at 23:51
  • It looses surface charge. – Solar Mike Sep 26 '20 at 5:10

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