Standard strongest battery for hoverboard. Fully safe and certified. 36V for 4.0 mAh.
Hoverboards battery are like any other lithium battery. They need to be charged after each time you use them and fully charged before storage. This information is in the instructions that came with the hoverboard. It's the same for anything that works with lithium battery, cars, power tools like drills or weedeater and even cellphones. Failure to do so will make the battery impossible to charge and useless.