Rechargeable batteries. What a great invention! They have made our life, at least, a bit simpler. We don’t have to bother running to the nearest store for buying new one, or a pair, each time they run out. Though they have long re-charging times, it is better than dumping packs of wasted batteries.
However, there is one serious downside of them. Never use them on wall clocks. Else, you wouldn’t know when their capacities have run down and you will end up happily gazing at the clock showing 6 in the morning while the bus you desperately need to catch to reach your office half an hour late, has just left the bus stop.
P.S.: Never use two batteries recharged at the same time on two clocks. Unless you want to know that nature and science do have a wicked sense of humor!!!