I was given a phone, a galaxy s. The battery indicator always shows that it is 100% charged. Not the end of the world but a bit annoying. I've not seen a way to fix it after a while googling.
Anyone got any ideas? Installing a battery app didn't work, I assume it is a hard/firmware not a software issue.
Try rooting and resetting battery stats through clock work recovery mode.
I still run an original galaxy s and recently stuck the slimbean ROM on it. This probably won't fix your battery problem but the phone will have the latest version of android and it will be pretty zippy. Its much better than any of the stock ROMs.
Have you tried a factory reset? I know in custom recovery mode you can reset the battery data, not sure if this is possible with stock recovery. It may be worthwhile flashing the firmware again using odin. You can download official Samsung firmware from Sammobile.com. The XDA forum would be the place to ask for further help.
Let the battery run down completely. Charge fully. Rinse and repeat.