TopGun - If you want to do it yourself, I used 1N4007 to do this. Can be sourced all over the place, just watch what you are being charged for it (should be just a few cents). Never had one cause an issue or failure of any kind. After installing, if it doesn't work, swap it end for end. Think of it as a check valve. It only lets power go through it in one direction. If you manage to install it backwards, the circuit will act like it's open.
So simple even I can do it..... (with no electronics background). -Al