Sanyou fishing lamp, can I change the battery and how to buy it?

Yes Fishing lights are generally 18650 lithium batteries, which are sold online. You can ask the seller to weld them for you because they can weld them cold. They don't have that equipment. Welding with electric soldering iron will affect battery performance. It is recommended to buy genuine Panasonic 18650 batteries. It's a little expensive, but it's not generally durable. I bought two Panasonic ones myself, and they are still very powerful after more than three years of use. Generally, sanyou lamp uses four batteries 18650.