the cartridges use a cr2025 lithium battery to keep track of the time and to power the sram save mechanism. as these games were released over 15 years ago, the original battery is usually depleted by now. it is possible to replace it, but it requires a special screwdriver bit to open the cartridge and soldering in a tabbed replacement battery. replacing the battery will erase the game save on the cartridge, if any, unless special precautions (such as backing up and restoring the save file using special hardware, or wiring a temporary battery in parallel with the original while removing it) are taken.