Poor Man’s Dual Battery

[Mighty Dodge Ram]

I know this topic has been beaten to death but I’d like to run this by those with more experience. I want to run a second battery in the bed of my 2002 Chevy 2500HD long bed. The PO had a Lance Camper attached with the Lance 12v electrical “pigtail” at the front of the bed, driver’s side. The pigtail has 8 gauge power/ground wires. Standard solenoid isolator located under the hood. Current truck configuration has a Leer topper that I sleep under, very simple setup.

Plan is to connect the pigtail with the 8 gauge wire, using ring terminals, to a 120 ah marine battery placed inside a typical plastic battery box located in the bed of the truck. The only load placed on it will be a 50qt ARB fridge also located in the bed. This will be for a 7-day desert trip, Mojave Rd/Death Valley beginning of June, temps already “warm”.

So...do you think this setup will adequately recharge the aux battery while driving under these conditions and for this length of time? Future plans include solar, etc. but I’m not quite ready to pull the pin on that yet. Thanks in advance for your responses and assistance.

Richard

 

[rando]

This should work OK for now. The one addition would be to make sure you have a fuse/circuit breaker on the battery in the bed (and at the other end, under the hood, if there isn't already one there). Maybe also leave a window in the topper cracked for ventilation while driving if you are using a non-sealed battery.

 

[alano]

I think the questions you need to answer are:

1) How much current can your truck provide to the aux battery when your driving?
2) How many hours of driving are you planning on doing each day?
3) How much current does the fridge draw when it is cycling?
4) Given the heat you expect, how many hours will the fridge run each day?

An ammeter can help you figure out the current questions. Your plans can help you with the driving hours. Not sure how to answer the last question without some sort of test or experience.

You have a nice big battery, but if the fridge draws 4 amps when running (my wild-ass guess) you only have 15 hours (until the battery is drawn down to 50%) of reserve. On a hot day in the desert, you're looking at not even 2 days if you don't recharge it every day. If you drive enough to recharge it fully, you should be fine. Remember that the fridge will run some of the time while your driving and reduce the amount of current recharging the battery.

Alan

 

[Mighty Dodge Ram]

Thanks for the quick responses.

Rando: for the fuse at the aux battery, is that on the hot line going into the battery or out of the battery? The ARB has its own fuse.

Alano: according to their documentation, the fridge draws about 0.87/hr. I’m sure that would increase in hot weather but hopefully I have enough amp/hours to cope. Stories seem to indicate several days on a charge and we’ll be moving each day, but there will be stops.

Again, thanks!

 

[rando]

That is on the hot line going to the battery that runs to the front of the truck. It is a large wire that (presumably) runs under the truck to the engine bay. If that were to be damaged under the truck and short the to the frame, you could easily start a fire. The fuse/breaker prevents this. Size the fuse for the wire - 50A for 8AWG.

 

[alano]

Ah, if the fridge draws less than an amp, you've got no worries. You can run it 2.5 days full time before the battery gets unhappy.

Have a great time!

Alan

 

[ntsqd]

Wasn't clear to me reading this fast, so I'll say just in case. There needs to be a fuse or breaker at both batteries.

 

[Mighty Dodge Ram]

Incorporating all suggestions. Thanks!