I bought a cheap charger from DealExtreme for my 18650-size lithium ion batteries. My other cheap charger will charge most 18650’s (though some are probably too long to fit), but it uses a lower charge rate that would take forever to charge up an empty battery. For instance, the small charger uses a 300mA charge rate and an 18650 battery is 2400mAh, so it would take 8 hours to charge that battery at a constant 300mA. And my big flashlight uses two 18650’s and the little charger can only charge one at a time.
So I found this other charger for $7.92 shipped that has two independent charging bays, supposedly charges at 1000mA, and stops charging at 4.20V like it is supposed to.
Here’s a review:
This charger looks cheap and is cheap, but it works. The bays are long enough to charge even oversized 18650’s. Mine are 67mm long and there are still a couple of more mm to spare. The cone-shaped springs are really weak so when you put a battery in, instead of getting pushed down, they just get pushed over.
The lights on the charger are bad, though you get used to them. For instance if you plug the charger in, the lights both light up green even without a battery. When you put a battery in, the light goes to red, indicating it is being charged. Once charging is complete, the lights will turn green. But if the battery somehow wasn’t making contact, the light would also be green. Oddly, when the charger isn’t plugged in and you insert a battery, both lights turn red. So if you weren’t paying attention and put the batteries in the charger unplugged, the red lights might make you think you are charging the batteries, when, in fact, they are slowly being discharged by whatever voltage it takes to light up the lights. I’m not sure why it wouldn’t have been set up so that the lights wouldn’t be on unless a battery was inserted, like with any other charger.
The charger is smart in that it uses a higher charging rate on an empty battery and then lowers the charging rate as the battery gets full. The charge rate is supposed to be 1000mA, but because it varies depending on the voltage I measured a charging current of 850mA with a battery charged down to just below 3.6V and it varied to less than 100mA as the battery was being topped off. Here’s a graph of time in minutes and the charging current and voltage.
This is a good thing, but this charger seems to take it to an extreme. I charged two batteries to 4.20V and let them sit. Two days later they measured 4.12V each. So I put them in the charger to top them off. One of the batteries took 30 minutes and the other took 50 minutes just to top off 0.08V. So this isn’t real fast. However, the gentle rate at the end of the cycle means I can use it to safely top off even my 600mAh 10440 cells after the smaller charger cuts off at 4.10V.
Charging 18650 batteries from 3.6V took it about 6 hours. That isn’t that bad except that you are supposed to keep an eye on li-ion batteries while they are charging in case they explode or catch on fire. So it shouldn’t be used as an overnight charger or while you are out of the house.
More often than not, I measure 4.21V on charged batteries instead of 4.20V just as the light goes green, but that is probably within the error of my multimeter. After topping off, there may be a 10mA trickle charge for a little while, but I couldn’t detect any current after 30 minutes.
The bottom line is that it is pretty cheap and charges li-ion batteries correctly. The fact that it has some quirks with the lights and takes a while is secondary.