What does it mean when my charger use to go down to 0.5 amps before it stopped charging a battery, but now with the same battery it goes down to 0.2 amps?

Most lipo chargers stop as a fraction of the set-point. Most of them have 2 modes, reg and "fast". Fast terminates earlier because it uses a higher current.

It's perfectly normal for current readings to fluctuate a little during charging. It is simply showing minute changes while charger is checking voltage and increasing/decreasing charge current.