Putting a battery disconnect on the positive cable so you can completely disconnect everything that may be a parasitic draw is the first thing I did when I bought mine home. Full charge, use switch to disconnect and recharge if I don't get it fully charged on the water. My dash lowrance shows the voltage for the starting battery on screen. I purposely hooked my smaller bow lowrance to the two group 27 TM batteries so I could monitor their voltage as well. Quick turn on them on and I get a reading and can identify if I need a charge on either system.