I was informed by Kirk from First Place Engines that Bill from c and h recommends not to use 6 volt Metal Hydrate batt on his ignitions nicads is ok the reason being the metal packs are charging up over 7 volts on a fresh charge and could damage the ignition . I have since to all 4.8 metal packs i am sold on metal packs have been using them for 2 years now no problems at all.