Low dc refrigerator

[mbruce]

Would a single house battery cause a low dc on frig when not plugged to shore power, engine running or generator?

If second battery is needed, would I wire positive to positive and negative to negative?

[Morich]

Lots of details on several things need to be given some thought before you can get a good answer.
Some of the things that are involved:
How much power the battery is designed to store (amp hours rating?)
How good shape as age and how it has been treated changes the answer a whole bunch.
An old battery that has been treated very good, may be as good shape as an
almost new which has been allowed to run dry or fully discharged!
How much power does the frig use per hour?
This will be an estimate at best, since a lot of things change the answer like how
hot is the weather and how many times does the frig get opened?
At some point the battery WILL run down and cause low voltage but how long do you mean for it to last?

Since a battery is just a way to store the power, the question is somewhat like asking how long a bucket of water full of water with a leak will last. Without knowing lots of things about how it is used, there is no real way to say how long before it goes dry?

[DavidM]

Is this a DC powered compressor frisge, a residential 110V AC fridge running on an inverter or a traditional absorption (propane) fridge.

To answer your last question: If your existing battery is 12 volts (and if you just have one then it has to be) then wire the second 12V battery + to +, - to -.

David