Name:   Pontoonfisher - Subject:   Dual battery use question Date:   2/28/2020 8:29:19 AM

Your 70HP outboard does not have enough auxiliary capacity to keep your batteries fully charged especially if your running the radio and other devices while running.   You would probably need to run the boat for 10 hours to fully charge both batteries that are at half of their capacity.   You need to be leaving the dock with fully charged batteries from an on board charger.  

Also, best practice is to only use the both position in emergencies.  Running in the both position can hide a battery issue