Group 31 true deep cycle for Jeep JK starter battery to combine with NL Power Pack?

jacobconroy

Hillbilly of Leisure
Hi,
I know that there is another thread on the forum where a fellow installed a group 31 battery in a Jeep JK, but my intention is a little different and I wanted some experienced advice.

Currently, I have a "standard" lead-acid starter battery in the JK and a National Luna Power Pack in the back for running a Propex heater, Fantastic Fan, and National Luna Weekender. I find that the group 31 battery in the Power Pack (VMAxtanks SLR125 AGM 12V 125aH) will handle running the heater and fan for one night and drop from 12.7 to 12.3 volts in the morning (approx 3aH to run both without Fridge). I want a second group 31 for two night trips and space is very limited. I'm also tired of worrying about battery maintenance.

So, I intend to install shore power in the Jeep this weekend with a NOCO 10 amp 2-bank charger under the seat in an effort to maintain batteries properly and solve the problem of "did I run the Jeep long enough to charge the batteries on the way home?". Here are my ideas:

1.Replace the factory lead-acid with another VMAxtanks Group 31 (lots of work involved with this) and giving a NOCO bank to each group 31. Leave them connected all the time normally, and install a normally closed 120 volt triggered solenoid that will sense incoming 120v when the Noco is plugged into shore power and separate (and properly charge/maintain) the batteries when home. If I do this, will the two batteries have enough CCA to keep the 6 cylinder starting without destroying my batteries or causing any other problems I haven't thought of? This would give 250aH total, meaning that I have 125 at my disposal without dipping under 50% (12.1 volts or so...right?).

2. Dump the Power Pack and install both VMAxtanks batteries in the rear with a new mounting plate. Give each a NOCO bank and 120v NC solenoid to separate when charging, and a 12v NO solenoid that only closes the connection between the lead-acid and VMAxtanks while ignition is on (leaving the factory battery to the alternator and normal driving conditions)?

3. Wire the second VMAxtanks battery in parallel to the Power Pack (assuming I can find a place to put it) internally to circumvent the Power Pack's relay and voltage sensing electronics, and add a 120V sensing NC solenoid to separate them during NOCO charging? This would necessitate me turning the Power Pack breaker off before charging, but I do that anyway.

What do you folks think? I'd appreciate the advice.
 

john61ct

Adventurer
First off, I would go with a better battery. Flooded is better value, but if you really need AGM, go with Odyssey, Lifeline or Northstar. Ideally they both should match, but not critical, can wait until the next one dies.

Starting an engine is hardly any load at all no worries.

To get best capacity, keep them combined as a single bank, nice fat marine wires, professionally crimped connections.

Put in an adjustable LVD cutout to isolate the Starter half when voltage drops to say 11.9, depends on the batt, may need to tweak that, experiment. Also carry a little jumpstarter powerpak fully charged as belt & suspenders.

They should be combined automatically when any charge source comes online on either side.
 

jacobconroy

Hillbilly of Leisure
Hi,
Thanks for the input. What's an LVD? That's a new term in my research. I though it was very important to match the batteries. Battery stuff is confusing! :)
 

jacobconroy

Hillbilly of Leisure
I'm not too worried about the cost, but I do want maximum aH. What would you guys choose between Odyssey, Lifeline or Northstar?
 

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