Bot 3 sets Lechmere closeout 10 years ago. Use sporadically and have experience that batteries last 4 years plus/minus. Buy a new one each year, keep 3-4 going. Inside batt are two industrial "C" Ni-Cads - older ones develop memory. To utilize best, discharge to 5% remain, then full. Not user replaceable. The torgue is enough to twist the unit out of a strong grip, but they are best for light/medium assembling, not all day heavy duty