RuBoy69 It is basically a volt meter. The different lights turn on when it detects different voltages (the item description lists the lights and voltage ranges) across the terminals (marked "+" and "-" on the board). To add this to a completed circuit or project,,, just have a small line from the positive of your battery and one from your negative side, and send it to this device. It just needs to detect the voltage-- you cannot pass voltage through it to power your device, if that makes sense.

RuBoy69 Yes. Li-Po and Li-ion cells have the same voltage ranges and charge/discharge characteristics. You can also use the same chargers, as long as you have the same number of cells and the correct "nominal" voltages.

RuBoy69 The description is assuming you are wiring in a series (the S stands for Series). If you have a combination series/parallel, it is different. If you have 6 cells and you measure 12v, then use the 3S model, because your nominal voltage is going to be 11.1v. 12 volts is normal, so don't worry- your voltage will range from ~10v-12.6v. You simply have 2 3S banks in parallel, so use the 3S version.

RuBoy69 For any single 18650 battery (including yours) or most LiPo batteries, use S1. Use S2, S3, and S4 for 2, 3, and 4 cells in series, respectively. If they are in parallel, just use the one for that nominal voltage (S1=3.7, S2-7.4, and so on).