Well, I charge them when they run out, usually! I have more than one going at a time, I have counted up to 8 at once, all with different flavors, of course.... Most of them are egos, so I never really know when they are going to run out... Hence, the inverter for the car! Luckily, we haven't lost electricity in a while... But, often I have several things to charge at once. Like now, lol!