[ostaF]

 

[bestatchess]

Remove battery from vehicle, connect to charger and fully charge, disconnect from charger and rest with open terminals for 12 hours.

State of charge can be estimated from open terminal voltage. Generally speaking, for 12V lead acid starter batteries, 12.65 and up after 12 hours rest is 100% charged.

Battery Tutorial

 

[Walrus]

You don't use a MM.
You use a load tester.
I bet you can buy a load tester for 12 bucks at HF tools.
Autozone, or pretty much any other nationwide parts store will load test it for free.

 

[VQP0WER]

walleeme is right. Multimeters will just tell you voltage, but not amperage. The battery could read 12-13v, but soon as you put a load on a weak battery, it will go down.