Added a second battery, drained both! (BATTERY HELP)

[AZMark]

Keep in mind that if this switch doesn't have an OFF position you'll have potential issues with any parasitic draw. This is a 4 way that shows the OFF. Cant tell in your photo if you have that option or not.

View attachment 128486

I was thinking the same thing but didn’t think it would make sense for one to exist without an OFF position. Optical illusion?

 

[Miitch]

Keep in mind that if this switch doesn't have an OFF position you'll have potential issues with any parasitic draw. This is a 4 way that shows the OFF. Cant tell in your photo if you have that option or not.

View attachment 128486

Yes, the switch does have an off position! Camera angle hides it

 

[nbiongo]

My goal was just to have a “larger battery”. Just so it didn’t die while anchored playing the music through the new speakers. The switch was off, and then the next morning both batteries were dead. So a new 3 way switch is the way to go ??

this is the setup I used to add a 2nd battery to my boat. Use a 1/2/All/off switch

 

[Dixemon]

All good info, ill just add that using 2 different battery ages, chemistry or capacities will not work on the same circuit. Reason being is that one will always act as a resistor in the circuit and prematurely drain the other battery resulting in a failed power system. Not only that, but they would never charge correctly wired in parallel. Also, if not a sealed acid or gel AMG type battery, you need to check your electrolyte biannually. If one of the cells get dry it will ruin your ability to charge and absolutely kill your available amps. you can check for dead cells with a hygrometer.