We think that these little testers are the best thing since sliced bread ! You can test the current drain on any circuit, simply by removing a fuse and inserting the plug. In the case of a bike with a fuse in the charging circuit, you can even test the current the alternator is putting back into the battery. It will measure up to 20amps which is just what you want on a bike. Most multi-meters only test up to 10amps DC, which often isn't enough on a charging circuit.If your bike doesn't have a fused charging output from the regulator/rectifier it is worth fitting an in-line fuse holder, not only for safety, but also as a <port < to easily test the charging current. We've been trying to think of a way to overcome the difficulty of testing bike charging for years, and we think that this unique solution is sheer genius.