You are probably wasting your time and endangering the charger and obc by messing around with a bypass.... You have used a car charger to get the batts up to where they are now, correct. but they are dropping 2 volts in 16 hrs. I could almost garrantee they are never gonna come back after 2 years of setting.... Never seen it happen yet. If you doubt you need batteries go to auto parts house and get a simple hydrometer and test the
specific gravity of each cell. Probably find 6 bad batteries? Simple easy test
Post your findings here .....