Battery capacity recommendations--amp hours

RollinWithShirley

When I am towing all day and running my refrigerator, sometimes the battery is dead at the end of the day.  The battery charges up on shore power and/or solar.  I had the battery checked out and they said it was charging fully but suggested that maybe I need a battery that provides more amp-hours.   My current battery provides 85 amp hours, but they have one that gives 120.   It is a deep cycle, no maintenance battery.  I expected that the charge from my towing vehicle would sustain the fridge when it is turned to battery.  Thoughts?

qhumberd

I know that the answer to your last comment on the charge from the tow vehicle maintaining battery charge when towing all day is "it depends". But it should not be hard to determine. After I put a shunt in my 400, I could tell immediately that my TV would start adding about 2 amps to the battery when at idle and the battery was on and just the baseline loads were being drawn from the battery. We have the 2 way smaller frig and when it switches on it draws between 4 and 5 amps from the battery. However it only runs for 5-10 min per cycle depending on the exterior temps. So if it runs a couple of times per hour I run a deficit for 20 min and then for 40 minutes it recovers. Most summer days of towing I have lost little to no battery capacity when I arrive to camp.

If you have the larger frig I have read that the amp draw is considerably more and this could over 6 hours of driving leave you in deficit but I still can't see how you would draw 85 amp hours even if the frig and all else was drawing say 7 amps each hour and did not shut off. That would mean for 6 hours of driving the draw would be 42 amp hours total. Only about half of what your current battery provides. And that would ignore any solar input you get on the road.

So something is not adding up. Some more details may help the electrical gurus here.

Sharon_is_SAM

@RollinWithShirley - if you still have your 2015 TaB S Boondock, the 3 way frig on battery draws about 11 Ahr, so it will deplete an 85 Ahr battery over a longer towing day.  There are other ways to keep the frig cool including precooling on AC, packing it with frozen water bottles,etc.  If your tow vehicle is like many, it will not be able to effectively keep up with the battery drain.  Also, if you have run the battery down multiple times, you likely need a new and larger battery.  Some owners run their 3 way on LPG while towing.  

BrianZ

We pre-chill our frig on house AC power starting the night before we leave home, then put frozen bottles of water and just a few other pre-chilled things inside & turn off the frig before leaving.  We keep the bulk of our refrigerated items in an ARB frig plugged into 12V outlet inside our vehicle while on the road. (It's compressor is a lot more efficient than the power-hungry T@B frig on DC).  At the campsite, we run an AC extension cord out the window from shore power to the ARB; or if no shore power, the ARB is connected via DC cable to our 150AH trailer battery with solar panel to maintain charge, while running our 3-way T@B frig on propane.  So, we never run our T@B frig on battery power.  We just have to remember to unplug the cable to our ARB before taking off anywhere in the vehicle!  It remains plugged in to the vehicle 12V outlet which is only powered while vehicle is running.

We started using our ARB frig at home during the pandemic to stock extra cartons of milk & OJ etc, to minimize grocery shopping trips, and my wife has refused to give it up.  It's a bit of a pain to lug around for home use (otherwise would stay in the TV), but worth the investment to us to have all the frig space we might need, very cold food & drinks, and without needing to buy ice.  So, bottom line is that we just don't bother trying to ever use the T@B frig on battery (although the solar might keep up on a good day with full sun, if we had to use it, like for a temporary lack of propane).

GigHarborTom

I do not run anything on propane while on the road. A bit concerend about safety with the exposure at the gas station etc. When we seldom boondock, we run the frig on propane. We precool the frig the night before departure with jugs of frozen water. Our rig when home is in storage facility without power. Usually once on the road, we fire up on DC. We have had no issues with old or new batteries failing. We for the first time, have a Renogy battery. (Came with the recent Tab purchase.) Had a huge 48 quart cooler ( ice) that we gave the kids. We now just have a small cooler that does us well. We have been on some long trips with our former 2003 and now 2019 4Runners, different trailers and have had no problems. We did have a tempermental  3 way frig in a Casita years ago. Sorry not much help.

VictoriaP

RollinWithShirley said:

When I am towing all day and running my refrigerator, sometimes the battery is dead at the end of the day.  The battery charges up on shore power and/or solar.  I had the battery checked out and they said it was charging fully but suggested that maybe I need a battery that provides more amp-hours.   My current battery provides 85 amp hours, but they have one that gives 120.   It is a deep cycle, no maintenance battery.  I expected that the charge from my towing vehicle would sustain the fridge when it is turned to battery.  Thoughts?

I’ll add that your current battery sounds like a sealed lead acid, not AGM and certainly not lithium. If that’s true, the amp hours available to use without damaging the battery are 50% of what’s on the label, so in your case, you’re trying to run a fridge that draws 11aH on a battery that really only has 42.5 available. It won’t take a very long drive at all to run that down, and a 120 won’t give you the big upgrade that it appears to on first glance, unless it’s an AGM.

AGM batteries can safely be drained further (70-80%) without damage, lithiums can use 90% of their capacity. So you want a battery that’s actually designed for that kind of use. But even so, trying to run the 3 way fridge on 12v is a recipe for a dead battery when you arrive at camp, in most cases. If your tow vehicle is anything other than a big truck with a good tow package from the factory (including an oversized alternator or second alternator, and very thick 12v wiring, not just a hitch), odds are you won’t be able to keep up with the demand from that fridge. With most cars nowadays, you’re dealing with “smart” alternators that aren’t smart enough to charge the trailer battery, and a barely powerful enough to charge the vehicle battery. Bigger alternators can cost you MPG, so they’re carefully sized to the vehicle as it was designed, and not to charge a second battery bank. There are ways around this, but it will take installing a DC-DC charger, not just putting in a new battery.

Which is why everyone is offering up alternatives. Personally, I’ve seen too many RV propane fires by the side of the road and in the days when used to scrounge at RV salvage yards; running on propane while towing isn’t a solution for me, and isn’t legal is some places. I’ve used a regular cooler in the car, a 12v fridge in the car, and my personal favorite, frozen bottles or ice blocks in the fridge with the fridge off for the duration of the drive. The ice trick works well for shorter drives of a few hours, for anything longer, I’ll drag the 12v cooler along.

AnOldUR

BrianZ said:

 ... if no shore power, the ARB is connected via DC cable to our 150AH trailer battery ...

For longer trips we also carry a 12V chest fridge/freezer in our TV. While traveling it's plugged into the TV cigarette lighter outlet. I added a cigarette lighter outlet to the front of our tongue box to be able to plug the chest fridge into at a campsite. We also can run the cord out the back of the TV and plug into the trailers battery. Good for one night stop when not disconnecting and not wanting to run down the TV battery.

(see the dual waterproof outlet just below the T@B emblem on the box)

RollinWithShirley

VictoriaP said:

RollinWithShirley said:

When I am towing all day and running my refrigerator, sometimes the battery is dead at the end of the day.  The battery charges up on shore power and/or solar.  I had the battery checked out and they said it was charging fully but suggested that maybe I need a battery that provides more amp-hours.   My current battery provides 85 amp hours, but they have one that gives 120.   It is a deep cycle, no maintenance battery.  I expected that the charge from my towing vehicle would sustain the fridge when it is turned to battery.  Thoughts?

I’ll add that your current battery sounds like a sealed lead acid, not AGM and certainly not lithium. If that’s true, the amp hours available to use without damaging the battery are 50% of what’s on the label, so in your case, you’re trying to run a fridge that draws 11aH on a battery that really only has 42.5 available. It won’t take a very long drive at all to run that down, and a 120 won’t give you the big upgrade that it appears to on first glance, unless it’s an AGM.

AGM batteries can safely be drained further (70-80%) without damage, lithiums can use 90% of their capacity. So you want a battery that’s actually designed for that kind of use. But even so, trying to run the 3 way fridge on 12v is a recipe for a dead battery when you arrive at camp, in most cases. If your tow vehicle is anything other than a big truck with a good tow package from the factory (including an oversized alternator or second alternator, and very thick 12v wiring, not just a hitch), odds are you won’t be able to keep up with the demand from that fridge. With most cars nowadays, you’re dealing with “smart” alternators that aren’t smart enough to charge the trailer battery, and a barely powerful enough to charge the vehicle battery. Bigger alternators can cost you MPG, so they’re carefully sized to the vehicle as it was designed, and not to charge a second battery bank. There are ways around this, but it will take installing a DC-DC charger, not just putting in a new battery.

Which is why everyone is offering up alternatives. Personally, I’ve seen too many RV propane fires by the side of the road and in the days when used to scrounge at RV salvage yards; running on propane while towing isn’t a solution for me, and isn’t legal is some places. I’ve used a regular cooler in the car, a 12v fridge in the car, and my personal favorite, frozen bottles or ice blocks in the fridge with the fridge off for the duration of the drive. The ice trick works well for shorter drives of a few hours, for anything longer, I’ll drag the 12v cooler along.

RollinWithShirley

Thanks so much.  We do have an AGM battery but it helpful to know that this is a common issue for long hauls and we will try some other tricks before getting the bigger AGM.   I don't want to drive with the propane going, but thought I might try turning the frig off at some intervals to let the charging catch up.

RollinWithShirley