Warning- If one of Skinny Water Marines-approved chargers ( 12v charger ) for one battery, ( 24v charger  ) if combining two batteries, ( 36v charger  ) for three batteries, are not purchased or used with the battery, Skinny Water Marine is not responsible for your battery not charging properly. Many of the labeled lithium chargers on the market are not set up to charge our batteries at the correct voltage. We highly recommend to purchase and use our chargers only.