Review on Skywolfeye 10-Slot Universal Smart Battery Charger for 3.7V Li-ion Rechargeable 🔋 Batteries - Compatible with 18650, 26650, 14500, 16340, 18500, 10440, 18350, 17670 Batteries by Rich Fiedler

I recycle thousands of Li-ion batteries. Part of the recycling process is charging them to test their capacity and internal resistance. I tested 2 such devices. They are unmatched in price and functionality. They get pretty hot as many have commented. When you lift them, the heat is dissipated. Reverse polarity protection works. I used to build my charger array from TP4506 boards, but at $1.40 per charger, buying is better than building. Also, most TP4506 boards do not have reverse polarity protection. The most egregious downside is that they constantly overcharge the cells to 4.24-4.26v on both of my devices. Some testers like the Zanflare C4 refuse to test cells at this high voltage. OTOH, it might be ok if you only use them for a one time fee. The next problem is the heat generated during charging. Prolonged exposure to heat shortens the life of the lithium-ion battery. Therefore, with regular use, the combined overcharge voltage and heat will significantly reduce battery life. It's not the main charger for me so it's ok.