Mobile Battery Pack vs Hardwired Dual Battery Setup

**Feel free to just read "THE QUESTION" and the "2nd Question" if you're just popping in a for a sec and can help**

Looking into this whole "I want to power things when my truck is off" has sent me down the rabbit hole. Before I started looking at all of this, I didn't know anything about electricity, wiring, etc. Hell, I still might not know, I just think I do. That's what has brought me here to post this thread. I feel like I know enough now to at least ask a semi-coherent question. Here we go:

Dual battery setup cost a lot from what I have gathered and limits you to always be near your vehicle. However, you can run larger (more Ah) batteries then the mobile counterparts. Being mobile is nice and allows for a little more freedom at the cost of a smaller (less Ah) battery.

THE QUESTION:

• If I have a fridge that pulls at 1 Ah, and a mobile battery that is rated at 240 Wh, in theory, would I be able to run the fridge for 20 hours without any issues on the mobile battery pack?

What I think I would like to do is, have the fridge plugged into my single battery truck while I drive to the destination and even while I'm setting up camp for the day, etc. Then unplug from the truck and plug into mobile battery pack, either at the truck or at a campsite away from the truck for the night (8-12 hours). Then charge the mobile battery pack during the day via solar and have the fridge plugged back into the truck (either moving or not). And keep doing this cycle while we are out camping, hunting, etc.

2nd Question:

• How many Ah's does the factory 27F battery have?

From what I understand, I want to keep it above 50%. Again, anything I've learned on this subject is just reading on the web. If I'm wrong on anything, just let me know. I might ask a dumb (to you) question about something (if I already haven't) but it's because this is all new to me and I'm trying to learn. Thanks!

 

Per your second question: it depends. Auto batteries are rated in cold cranking amps (CCA) not amp-hours or watt-hours like a rechargeable tool battery would. We don't usually care about the "capacity" of the automotive batteries because that usually doesn't matter. All that matters is that the battery has enough amperage to start the car and it is assumed that the alternator takes over from there.

Hopefully this link will help guide you a bit, there are ways you can find capacity using some basic tests and a multimeter.
https://batteryscout.com/how-many-amp-hours-in-a-600-cca-battery/
https://sciencing.com/determine-ah-12volt-battery-7733095.html

 

Thanks for the links. Wouldn't it matter to know the Ah's on any given battery if you are going to be running something off of it while not directly getting power from another source? Alternator, solar, generator, etc. I get what you are saying though, that it's not the intended purpose of the manufacturer for you to be using your vehicle battery in this way.

 

Yeah, I'm not saying it doesn't matter. What I mean is it doesn't matter to the manufacturer, so they don't list that information. If you look at aftermarket batteries you should be able to find data sheets with more information, I'll see what I can find.

 

I agree with you. Was hoping someone had that information. I can't seem to find it. Northstar is really good at listing all of their information including Ah. Will most likely be going with this battery when mine gives out.

 

I tried to keep my set up as simple as I could. I have the Dometic PLB-40 battery and Dometic CFX50 fridge. A northstar 24F battery is my sole battery in truck. When driving the PLB40 is powered by the truck via a 12V outlet and the PLB40 powers the fridge. When at campsite the PLB40 continues to power the fridge as well as charge various things like phone, gps, and bluetooth speaker through USB ports. During the day a 120W solar blanket keeps the PLB40 completely charged. If need be I can easily go 2 1/2 days without charging the PLB40 as you can run it down to 0 percent. The battery and fridge always stay connected. Plus being portable I can set it up in the house when PG&E decides to cut the power.

 

Perfect. Simple and I like it. Thanks for the information!

 

What solar blanket are you using? If you don't mind me asking.

 

The blanket is Overlandsolar's Bugout 120. I did my research and the only negative reviews had to do with price. Very durable and packs up so small, plus came with 2 20' cords and the connectors fit right into the PLB40. Didn't need a solar charger either since the PLB40 takes care of that. I'm quite happy with it but it is pricey.

 

If fridge draws 1amp. And you run it for 1 hour. You have just used 1 amp hour. So for it to run all day, you need at a minimum, a 24 amphr battery.
For 8 hours, at least an 8 amphr batt.
240 watt hours @ 12v = 20 amphr. But if it's a lead acid, you'll only get 50% of that usable. If it's some sort of lithium, you normally get 100% of it as usable power.