The most useless thing there is 1) Very bad cheap Chinese construction at a very high price 2) with full charge after 30 minutes you run out of battery. For professional use it is not suitable, I will buy another branded one from a specialized store that sells similar products and has knowledge. I would return the device that I have had for less than a week but unfortunately I threw away the box. To change the built-in battery type 18850, the whole device needs to be opened as shown in the photo only by a professional. Those who sell these devices should withdraw them or sell them for no more than 35 euros. I hope I helped consumers who do not know the product purchased from a store that is on Skroutz directly from the store's page