Rechargeable batteries can be a problem too, a friend of mine charged some "AA"'s in the correct charger overnight and woke in the morning to a horrid smell , on entering the kitchen he found the batteries were a pile of smoldering ash ! , After a cool down he scraped the charger out and checked its output on and off load, all was well with the charger , turned out he had bought the rechargeables from the pound shop .