Electrics: Vida/ battery Advice

[SwissXC90]

Originally Posted by glengibson

what voltage should I be getting on the battery?
tried a multimeter was getting 12.1v (nothing turned on)
engine running was getting 14.4 v
tried cranking it, dropped to about 10.2v

thank you

14.4V when engine running and charging is normal

A battery can drop to very low volts when cranking, you need specialized fast acting voltmeters to see what it drops to, so 10.2 is likely normal.

When measuring the battery voltage with the key turned off you need to understand if the car is still using power. A lot of components stay active for a few minutes after you turn the key off and then slowly shut down. After around 10 minutes the car has fully gone to sleep, provided that no doors are opened at that time. Each action of opening a door wakes the car up.

So to measure key off battery, connect the volt meter to the battery or the jump start engine connections, and then wait.
One way to know when the car has gone to sleep is to leave the boot open and observe the boot light. It goes off when the car goes to sleep.

Only then is a key off battery reading meaningful.
A good battery will sit at around 12.7 volts with no load. The correct method is to wait 24 hours after the last charge for the battery chemicals to stabilize.
If at 12.2, the battery is either weak or being loaded because some of the car is still drawing power.
On my car battery, when at or near 100% charge, the battery voltage will drop to about 12.6 or 12.7 V when the key is off but car is still using power, and then slowly rise when the load reduces to around 12.7 to 12.8V, and then slowly drop over time to about 12.7V the next day.

[gmonag]

The battery voltage should be 12.6V with no load.
14.4V is the voltage put out by the alternator.
When cranking, the voltage should not drop much below 12V.

You need a new battery.

Edit: Didn't see Swiss's reply - doh!