4 x 18650 Batteries Emergency Charger w/ LED Illumination Light / USB Port for iPhone / iPad - Black

Pros: * You can use 18650s you already own * You can replace defective batteries instead of throwing everything away if one breaks * Approximately 10.000 mAh are nice to have * As small as possible * Perfectly decent quality

Cons: * You need to buy your own 18650s (if you don't own them already) * No manual

Other: A couple of friends already ordered their own - a most useful and cost-effective thingy.

Pros: - Cheap - 2A output - PCB contains battery protection circuitry (deep discharge, overcharge, short circuit) - Bypass diode from input to output - Step-Up converter efficiency of 70-80% - Trickle charges deep discharged batteries - Doesn't start charging if battery voltage is above ~4.15V - Fuel gauge isn't all the way off (but tends to be a bit too optimistic)

Cons: - Efficiency isn't excellent, but acceptable - No true CC+CV charging, you won't get >1A charge current at battery voltages above about 4.1V - PCB build/assembly quality isn't the best, but certainly OK for that price - Unreliable charging indicator (sometimes it's green even though it's charging)

Other: Awesome product for that price, apparently well-engineered electronics. I'm really curious what that jumper on the PCB is good for.