I was wondering if it is safe to charge a hoverboard battery pack with the charger it came with externally? More specifically can I connect the charger directly to the battery? The battery is a 36v 4.3ah which I believe has a BMS. The battery has only a positive and negative wire coming out of it. The charger is rated at 42 volts at 1.5amps.

 

The battery should have a protection board, but those rarely ever include circuits for lithium charging; they just disconnect to protect from overcharging. If the charger has an LED that changes color when the battery is full, it very likely is a charger rather than just a constant-voltage power supply. It'll usually say something on the label about being a lithium charger rather than just power supply.

 

It has a color changing led that turns green when the battery is full. Thank-you for your input.

Something I found and did not understand: when measuring the battery's voltage with a DMM, I would get a reading of 18.6v for a fraction of a second, then a reading of 10.8v then less, then less all for a split second. When connected to the ebike, the battery would work.