The 12V rechargeable drill must be a lithium-ion battery or a nickel-metal hydride or nickel-cadmium battery. The battery is made up of several cells connected in series. In the situation you mentioned, one of the cells must have leaked. or exploded. The reason is that if you put multiple batteries and chargers together, the positive and negative terminals of the battery are directly connected by metal conductors, causing the battery to externally short circuit, excessive current, heat, etc. cells are burned. It is recommended to use a multimeter to measure whether the voltages of the two batteries are different. Don't use the problem one. In the future, batteries can no longer be packaged in this way, just as cell phone batteries cannot be put in pockets with conductive objects such as keys and credit cards. This is very dangerous.
1. First of all, the rechargeable lithium battery has four connectors, the upper left corner and the lower right corner are used for charging.
2. Second, make sure the battery and charger match before use, and be careful when using a charger with imperfect functions.
3. Finally, avoid damaging the battery and charging it improperly.