Really tough to determine what the actual question is without some punctuation but here goes. First, Perko switches usually have four positions, not three. They are: OFF -- BAT 1 -- BOTH -- BAT 2. OFF obviously removes both batteries from whatever loads are connected to the COM terminal on the swtch. If you are experiencing excessive load in what you are calling the START position then that battery very likely is not capable of providing the current needed. The reason may be because the battery is too small, not being charged, or is simply headed for battery heaven. Using the BOTH position (ALL as you indicated) applies both batteries to the system so the perceived problem goes away. Why not try the BAT 2 position and see if things work ok. If it does, then BAT 1 is bad or not charging. The BAT 1 and BAT 2 positions supply whatever is connected to the COM terminal. The best setting for the switch is to alternate between them so either one gets used and charged on a regular basis. Using the BOTH position is ok but why not put the full alternator charge to the battery that needs it most rather than attempting to charge both batteries at the same time. You might also check and clean all of the battery connections to ensure corrosion isn't causing the problem.
