[TrainSafe]

84% doesn't mean anything. Could just be the last charge state.

I'd give it a few days to see how it performs. I've also gotten free batteries from my local Sprint store. They're usually take-outs from phones that have been returned or found defective. Some are only days old, and some might be half worn out. The only reliable way to tell is to use them.

My policy: a free battery is a good battery!