The manual does show it will take a freshly charged 6 volt pack at 7.2 to 7.4 volts which drops pretty quickly as soon as it starts feed power and a quick call to Dave at DA confirmed this once I got my first one.

7.4 Volt lithium packs are fully charged at 8.3 to 8.4 volts and take a long time to get down to 7.2 to 7.4 volts and this would cause problems with the DA module. I like the 3W engines because you do not need to regulate the ignition and they even say that it can cause problems if you do