1S 2S 3S 4S PCB BMS Protection Board 3A 20A 30A 18650 Charger Protection Board Module Overcharge Protection for Drill Motor. rotect your lithium battery packs with this reliable BMS board. Available in various configurations (1S, 2S, 3S, 4S) and current ratings (3A, 20A, 30A), it offers overcharge, overdischarge, and short circuit protection for your 18650 batteries.