Review on 4-Pack 18650 Battery Charger Protection Module, Power Bank PCB Module Board, Dual USB 5V 1A 2.1A with BMS Protection for DIY Phone Mobile Power Bank by Kevin Cota

Received all 4 boards with no problems. as long as it was connected to the board! If you unplug the battery from the board and then plug it back in, the estimate won't be accurate until you've done at least 1 more full power cycle. I use one of these to power my Raspberry Pi with a single 18650 battery. A 2500mAh 18650 battery powers the Raspberry Pi for 4 to 10 hours depending on system startup and whether USB devices are connected to it. These battery regulators seem to estimate battery life pretty well, within 10% I'd say, but there's no numerical data or evidence to back it up. The second board I'm using has 3 18650 batteries connected in parallel powering a battery regulator. , actually a 7500 mAh battery. I was concerned that the battery percentage estimate would be very inaccurate when using batteries in parallel, but it still seems accurate to about 10%. With these 3 batteries connected in parallel, I can fully charge my phone about twice (10). % battery to 100%) with a 3200 mAh phone battery. So between this converter and the phone's battery regulator, the USB port's 2.1A conversion efficiency seems to be at least 80%. (-) n/a I didn't take any measurements, but the holes were just big enough for my wires to fit through. I used random pieces of wire, so I don't know the caliber offhand. 18 gauge I assume?