3PCS 18650 Lithium Battery Multi-Cell 2S 3S 4S Type-C to 8.4V 12.6V 16.8V Step-Up Boost LiPo Polymer Li-Ion Charger 7.4V 11.1V 14.8V （2S-4A）

Mine were 4s lithium ion. Perfect solution. Weirdly needed a correct wire. If it doesn’t work try a different wire and block. No idea.

Absolute trash. Heats up to unsafe levels and shuts down, I actually received a burn from this product.

They work great and arrived very fast, and are exactly as advertised!!!

Alex H. is right. You can only use this device with dumb 5V USB power. Basically, it will work with USB-A to USB-C charging cable that comes with some devices.If you connect it to a real USB-C power adapter (like one from a laptop, MacBook, or other high-power demand devices), you will get no power -- for the reasons Alex H. mentions.This is the 4 amp 3S version that appears to draw far too many amps from a typical USB-A power supply for it to be able to charge 3S 18650 cells.I will try the 1 amp 3S version to see whether the lower amperage will keep my USB-A power adapter from overloading.[UPDATE: The 1 amp 3S version worked fine for recharging three 18650 cells in series (3S). It isn't fast charging by any means -- it took about 12 hours to charge the cells -- but it stopped charging at the correct voltage level. The 1 amp version got a little warm, but not worryingly so. Now that I'm getting over the disappointment that these devices don't work with "real" USB-C voltage auto-detecting power supplies, I'm finding them adequate for the price. I really wanted something that would negotiate a higher voltage, but apparently, this feature isn't available anywhere for dedicated charging modules yet.]-

Only works with true fast chargers. Led indicators are confusing. Both red and blue stay solid when it's charging correctly. Solid blue is either battery charged or your charger is not fast charger. Red flashing is wierd it's either battery not detected or not fast charger also. Also it gets really hot and it's not constant current it switches really slow. Make sure you test throughly I went through 2 moduels before I figured it out. I got it to work but it has to many caveats and the directions are unclear and it's just one of those things that I had to let the smoke out of two of them and spend a few hours on before I figured out how it works and now I know how it works and it doesn't really work great because it makes a lot of heat I would look for better options

I have a love/hate relationship with this product. First, it should not be offered in a 4A model. Can it output 4.2v 4A from a 5V supply.....technically yes. But that inductor get SO incredibly hot that there's not way it's going to last for any reasonable length of time without active cooling. At most, I wouldn't use these for more than 2A. Maybe in China it's easy to find a non PD (power delivery) USB-C adapter that can output more than 2.4A but those don't really exist as a quality product. The best I've been able to find is 5V 3A which isn't a normal standard for USB. Sustaining 4A from a 2.4A supply with only .8V of drop is a recipe for trouble. But I feel like you would need a 5V 5A USB-C (non QC or PD) adapter to make that work well. Ideally, they'd put a PD controller on this, charge $5 more and then you'd have a product that is actually useful.TL:DR; buy the 1A or 2A and stay away from the 4A. Use the best and highest amperage 5V only charger you can get.

Very small and useful

I might have not realized the 2 board were connected together in I hadn't read it in other reviews.A little more searching turned up a wiring diagram.Initially it was not clear to me where the charge and where the load connected. Other reviews clarified that the both the charger and the load connect to the P+ and P-. The BMS auto switches between input and output depending on the voltage on P+P-. I tested it on my Power wheels car and the full 20 plus volts were on the (P+P-) output terminals. With the charger connected for couple hours it raised the cell voltages from 3.6 to 3.8. One cell was at 4.0v . I will leave it on the charger overnight and see if it balances better.If you connect your load to B+B- , it will work but you will not have any load overcurrent or under voltage protection for your battery pack. You would be able to run your device till the battery is totally dead, which damages l-ion cells.