on a job i let the radio play. that usually is no trouble, for a good while. but i let the tailgate open for hours and killed my main batt.
lucky me, i tied in my 2nd batt and got started.
2 batts is highly recommended!,,,for me.

 

I installed dual batteries over 6 years ago. I wired them so all it takes is pushing a button and I can jumpstart myself.

 

yeah, i like your "ugly" connectors on the left!!
tell us about the button/ switch?,,source?

 

Military style connectors on the left. Tsunami connectors from Autozone on the right battery.

I installed an IBS dual battery monitor when I went dual.
Shows charge level in both batteries.
Auto-links the second battery for charging while engine is on.
It has a manual link button for linking when engine is off, like when I would need to jumpstart myself.

 

ok on ibs,,,too rich for me!. i charge the spare thru a big diode so it cant discharge with the main. i jump with short cable, a life saver!

btw my 2 batts are just sitting there om a homemade 1/8 plate bent to hold in place, 4-5 yrs ok..

 

An old style Ford starter solendoid can be used to link 2 batteries; hooked up to ignition, they link together for charging, but disconnect when the engine is off. That's how older RVs are set up to isolate the chassis (engine) battery and the house (camper) battery.

 

are those solenoids ok for continuous duty? most are used just briefly huh?
im thinking of using one with a button for ez jump starting, ezr that my cable i must attach. brief use just to start.

 

Mine, in my RV, is on the entire time I'm driving (at least 3-4 hour stretches). Both my current RV, as well as my previous RV was set up with the solenoid to isolate/charge the house batteries. 27 years, no failures.

 

ok good, i didnt think of using a sol, it would keep both batts the same, ill look in my barn/warehouse! for one.

 

A brand new one is only about $15 or $20. Google "RV battery isolator solenoid".