They are all internal battery sources. Some are replaceable and some are rechargeable. According to specs I've read, battery life appears to be "months", but fortunately most have a low battery signal they send. The bigger problem is that they need to use the cell network to send back. This can be defeated if you know what you are doing and suspect a tracker is embedded. Because of the cell network connection, most of the products are subscription based, which makes them impractical for someone with a fleet of bikes. One however, LightBug, appears to have a slightly more innovative business model where they only charge a fee if you ask for too many location checks over a period of time.