You just need to check with the manufacturer. The first one that I had with the warning didn't have all the circuitry - just the variable speed instead of fixed speed. That was a MinnKota almost 20 years ago and the manual had the warning to disconnect it before charging. It may just be to protect the manufacturers from a warranty claim in case something goes wrong and it gets cooked. I've been disconnecting mine ever since. It's easy unless you have the cables straight to the batteries.