12 volts at battery, but

What’s the deal? I’m getting 12 volts at the battery but then when you go to start it, it’s reading as if it were a dead battery?

Tester

There are two measurements of the electric power: 1) voltage; 2)amperage. The voltage is similar to the pressure at a water faucet. There may be 60 pounds per square inch of water pressure. Amperage, or current, is a quantity. Two faucets may be flowing at 60 psi, but one faucet is producing 2 gallons per minute and the other is flowing at 4 gallons per minute. Now, as you pull energy from a battery, the voltage will drop–possibly to 10 volts on a healthy battery. However, if the battery charge is depleted, the voltage may drop down much lower.

Suppose you put 8 D cell flashlight batteries in series. This would give you about 12 volts. However, this wouldn’t start your car as the amperage would be too low.

Your battery does not have the potential to provide the amperage required by the load. Your battery’s fully charged voltage (without load) should be 12.6 volts,you don’t even meet the no load standing voltage parameter.

Are you ready to get your battery tested (most likely replaced?) a “capacitance” test can be performed on a battery in a low state of charge,in order for a typical carbon pile load test your battery will have to be charged.

Step one. Remove and clean the terminals…How cold is it where you are? Batteries don’t do well when it’s below zero…How old is the battery? Five years is about all you get…

Then it is a dead battery. Or at least a broken one. I have seen bad batteries do that.

Voltage with no load means little. YOu are doing a load test if you are watching the voltage with the starter engaged. You can charge the battery with an external charger and check the specific gravity of the electrolyte if the battery allows, or do a load test. If it fails, the battery is junk.

Sounds like a dead battery. However, get a jump and check the voltage again. It should be somewhere between 13.5 to 14.5 with the engine running. If it isn’t, the alternator/regulator is bad.
Also, check the battery post connections, clean if necessary