I have a 4V Li-ion Screwdriver by Master Mechanic and it's been super handy for the past 5 years. Recently, I've been having problems where it occasionally stops rotating properly when I press the trigger. It still turns, but slowly, weakly, and only for a second. This usually only happens when a screw is already on tightly, back when the electric screwdriver was still functioning properly. It's fully charged, and not in the lock position either. Most tutorials online I've been able to find are mostly for battery replacement but mine seems to be working. Any ideas what might be wrong and how I can fix it?