I'm a tight bu##er when it comes to batteries. I buy 5 nimh 4ah batteries from Lidl, solder them in series and insulate. 1 in the battery box and a spare in the tool box. Ive been told many times it won't work, they'll over/under charge, you'll need a special charger. Well, after 7 years, I'm still waiting for the catastrophe to happen. It seems that the voltage in the cells rise sufficiently to lower the charge rate. I'll now wait for the flak. 🤗