The manual on my muse says its battery is 3.3-4.2v. Most of the chargers I have available are 5 volts but the apms vary from 0.5 amps -2 amps. is there any concern about using the 2 amps? I recently had to return my first muse because the battery was not fully charging and before I start charging the replacement I wanted to see if there are any recommendations on the amps for the charger.
You should be fine using any of the chargers in that range. Any standard 5V USB charger should work. The amount of current Muse draws during charging is limited by the hardware, so regardless of the current available from the charger, Muse will draw a fixed amount.