RE: P-70 Kero different battery booster pack
What KC said.
a) it is OK to use a High capacity NiCd or NiMh pack of the SAME voltage as the ECU battery for a booster.
b) Never hook packs of different nominal voltages up in parallel. The higher voltage pack will try to charge to lower voltage pack up the higher packs voltage with no controls or monitoring in place. At best it could ruin one or both packs, at worst a fire or pack bursting.