Troubleshooting car batteries

My car battery seems to be weak since a month. Specially in cold weather when i parked it for two or more days it failed to crank engine. I checked voltage that was 12.63 v, i think battery was fully charged then i thoroghly tested it by this way . I don't know why it's not giving proper voltage to car engine when voltage are sufficient.

by John1188
December 30, 2021

Open circuit voltage is a very unreliable way to check a lead/acid car battery as it will be high at no load even with a near dead battery. As the battery discharges the open circuit voltage falls somewhat (10%--20% or so) but the internal resistance rises so much that the voltage under load falls off drastically, so much that it will not crank the engine. As you probably don't have a hydrometer to check specific gravity the best course would be to check the acid level and top it up with distilled water if it is low then charge it with a good a good charger.

by Foxx
December 30, 2021

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