Hey Eddie,
I went back and read your post again. The boost mode on your charger is 12V, I've seen those before. It is not for charging, just starting, kind of like jump starting with a 12V car. The chargers I have, have a boost mode in either voltage, but not 8V. You might be able to start it with that, but I wouldn't try to charge it, if it was mine.
Take care!!
Andy