I bought the same battery a few years ago. The charge takes about 8 hours. My old backpack. The left side didn't charge any of my batteries. The left side will only charge if you rock it for 5 minutes until it's in the right place. Difficult to get the light to stay red to indicate that it's being charged from a completely dead battery. Then use it and it won't charge anything at all. So I thought maybe that would be the only thing. So I ordered another one. It arrived quickly, but after the first load, the same problem as the old one showed up. Both sides charge, which is good, but it takes a while to get the batteries in the perfect spot. In short, it works, but it's terribly finicky. If you have patience and some money, this will do.