: battery voltage



stoveguyy
03-29-11, 11:26 AM
older battery. had it tested at store. said it was ok but not great. had 1 occasion in jan where car would not start. -10F. so it has been drained recently. turn on ignition and dash says 11.1V. have flaky mini meter. could not get good reading from terminals. took off battery cables and contacted lugs themselves and got 11.9v. ugh. not good. car seems to start ok and reads 13.5-14v always. i know battery is probably due for replacement but is it common for dash to read 11.1 and car will start? so when dash says 13.5 running it is not right? its really 12.5?

Submariner409
03-29-11, 12:33 PM
A fully charged "12 volt' battery reads 12.6 volts - a dead battery reads 11.9 volts, both measured with the battery disconnected from anything and idle for a half hour. Normal automotive charge indicators run about 14.3 to 14.8 volts with amperage varying as loads in the car change. Steady highway driving, good battery fully charged, you should see 14.4 volts +/-.

If you're not seeing these running values, something is wrong with the battery and/or the charging system.

stoveguyy
03-29-11, 12:40 PM
just started car. idled for several minutes. 14.2v running. shut off car, dash says 12.5, 12.4,12.3---finally stopped at 11.2 after 1 min shutoff ? but there are some subsystems drawing power with ign on?

stoveguyy
03-31-11, 10:51 AM
i am getting new battery. i just could not get a good reading with meter on battery terminals. i cleaned off terminal exterior and finally got a steady reading. 12.17V. why it read 11.9 with cable disconnected is odd. maybe 1 cell is funky. shutoff car and it settles at 11.6 at dash. thats an improvement. am getting new battery this weekend.

stoveguyy
04-08-11, 04:40 PM
got new delco battery. 12.6 on bench. old battery was 12.3 after 2hr drive. put in battery and dash gauge still drops to 11.7 with engine off. but than who checks their voltage with motor off?

Submariner409
04-09-11, 09:52 AM
When you turn the car key ON you energize a slew of systems in the car - there is no way on earth to assess the voltage or condition of a battery while it is dynamically supplying electricity. The ONLY way to check the state of charge in a lead-acid battery is to completely disconnect it from any circuit - remove the positive cable - and let it sit for at least a half hour, then measure voltage at the terminals with a good VOM.

Just for grins and kicks, turn the key ON. Call up battery voltage. Let it sit for 30 seconds. Now turn ON the headlights - what happens to indicated voltage ? Now turn OFF the headlights. What happens to the voltage indicated now ?

A battery LOAD test places an incredible amperage draw on the battery and the test set measures power supply capability and voltage drop compared to elapsed time - if the battery will not put out XXX amps at XX.X volts for XX minutes, it's on its last legs.

Look at post #2. Both the running voltages and static voltage chart are correct.

For more insight, Google something like "lead acid storage battery theory", or "surrette battery" or "rolls battery" - those sites will have lengthy discussions on battery operation and maintenance.