Newbie needs Battery Advice

[Trester]

I am new to RV'ing and I really need advice on batteries. Most of my camping has been, and will continue to be boondocking. My problem is that my one group size 24 battery does not have enough capacity to run the furnace fan at night when it is cold. I can't add another size 24 battery because the space between the tongue railing is only 21 inches, the available height for a new battery setup can't be much taller than the size 24. . So my question is what are my best options for batteries that would give me the most capacity during the night hours for the furnace fans. I would really like to keep the batteries mounted on the tongue where they are currently mounted. Going into the night, the battery is always charged to full capacity. I realize that there are a ton of threads on the forum that could answer my question, but I know virtually nothing about batteries at this point.

Winnebago Minnie Drop 190RD
175W Solar panel on roof
Truck does charge battery while towing
3000/2300W generator.

[MatthewChase]

I have 800 amp hr of lithium that takes 3 days to discharge. I rarely even have to use the generator.

Get 100 amp hr LiFePO4 batteries from Alibaba.com. Don't buy the battle born at more than twice the price. You'll pay about $500 per 100amp hrs, but they are small, lightweight and can be recharged 20,000 times. They also don't need watering and can be charged at a high rate. Yes they are pricey, but will last forever and give you the most bang for your buck in the long term. It will also be a future selling point should you sell.

[twinboat]

Some GP 24 batteries only have 55 AH of capacity.

A GP 31 battery will have 100 AH of capacity and not that much bigger.

Trojan Battery makes a T1275 battery with 150 AH capacity, a little more expensive, but about the most AH from a single battery that may fit your situation.

Look them up, check the dimensions, and see if they will fit.

Your heater uses about 7 amps to run. If it runs 40 minutes per hour ( real cold ), its using about 5 Amps per hour or 5AH. 10 hours of heater running uses 50 AH, plus what ever other power you use.

[Mark_K5LXP]

Yep, one could throw a kilobuck or so of lithiums at it plus whatever you'd need to update your converter to go with them.

Running a pair of 24's would add a lot of operating margin compared to one, so that's an easy option. No other changes to the trailer configuration required.

An important part of the capacity equation is charging. You can't get out what you didn't put in, so some review of the charge regimen may reveal something you can do along those lines to make sure you start out with as much as you can before you need it. Might amount to adjusting genset operation, maybe some solar or just different operating habits. Per twinboats example, know what your heater draws over a typical evening rather than guess. From there it becomes simple math to determine your run times.

Would offer that if you don't have a battery monitor, even an inexpensive one can tell you a lot about your usage and remaining capacity.

Mark B.
Albuquerque, NM

[DavidEM]

Your cheapest solution is a pair of 6V golf cart batteries wired in series and mounted inside a single battery box bolted to your tongue. Noco's heavy duty twin battery box is only 18.25" wide so it should fit on your tongue.

These will provide 220 amp hours of capacity, or 110 amp hours usable at 12V when wired in series. This will let you go for 2,3,4 days depending on the size of your furnace (small ones draw about 4 amps while running, bigger ones draw 7 amps as discussed above) and how cold it is.

Lithium batteries are nice but are expensive and require an upgraded converter to charge effectively.

David

[Mark_K5LXP]

What happened to the 110 unusable Ah?

Mark B.
Albuquerque, NM

[Marine359]

Originally Posted by DavidEM

Your cheapest solution is a pair of 6V golf cart batteries wired in series and mounted inside a single battery box bolted to your tongue. Noco's heavy duty twin battery box is only 18.25" wide so it should fit on your tongue.

Lithium batteries are nice but are expensive and require an upgraded converter to charge effectively.

David

For $400 you can put two 100ah AGMs on the tongue which gives you 100ah useable.

You can mount two plastic battery boxes side by side on the tongue by screwing two lengths of angle iron cut to correct length across the rails using self tapping screws. Or, you can mount a long toolbox using same screws.

And, yes LiFePo4 is way more expensive. Not only do you need a new charger, but if you want an inverter, you need a transfer switch. And while your checkbook is open, you’ll probably opt for an inverter/charger. It’s starts to add up, but in my mind, it’s worth it because you’ll never have to replace LiFePo4, they charge very quickly at high input amperage, and they are nearly impervious to cold, and they’re half the weight of Any other battery. My lithium gives me three days boondocking without genny

[Marine359]

Originally Posted by Trester

I would really like to keep the batteries mounted on the tongue where they are currently mounted.

This toolbox fits nicely across the frame rails behind the propane tanks. It should fit two group 27 batteries. You’d need to cut in some ventilation. I use it for my ground tackle because I moved my battery into the pass thru. Also, I mounted it with L-brackets and short compression straps, so I can easily remove it. $120 on Amazon:

https://www.amazon.com/dp/B07GZM4GT6...ing=UTF8&psc=1

[twinboat]

Originally Posted by Marine359

For $400 you can put two 100ah AGMs on the tongue which gives you 100ah useable.

Actually you have 200 USEABLE AHs. Use 160 AH to be safe.

Battery manufactures list all AHs as useable. Someone started a myth that only half were usable and it carries on today.

Or, all battery manafactures lie about capacity.

[Marine359]

By useable, I’m saying if you discharge a LA battery consistently below 50% you will in fact shorten its life cycle. If you consistently discharge to 20% you will nearly cut the life cycle in half. These recommendations can be found on nearly every manufacturer website and on dozens of websites related to batteries. I have never seen any published information that says otherwise. I’ve never owned AGM, but had FLA in my last motorhome, and my experience was consistent with that. When I got my LiFePo4 the instructions in the box in bold letters cautioned against discharging below 10%, and stated that charging in below freezing temperatures would reduce battery life. Don’t AGMs and gels come with similar warnings? Any way 90% of the posts I have seen on this subject commonly use the term “useable” to mean the % SOC you should not discharge below. But your point is well taken, you can use all your amp hours if you want. Except the BMS in lithium’s will shut down the battery when SOC hits 10%.

[LETMGROW]

Build a battery box which can hold 2 GC2 6 volt golf cart batteries wired in series and put it in the bed of your truck when you are going boondocking. A couple lengths of 10 ga. wire and a couple connectors will let you connect to your 12 volt battery when you are ready to use the extra power.
When everything is hooked up the 6 volt batteries will charge right along with the 12 volt battery when the truck is running.

[Trester]

Thanks for all of the suggestions everyone, it REALLY is appreciated! After reading Twinboats comments regarding draw for the furnace fan, I realized that I am not getting anywhere near that usage from my 100AH battery (Walmart's Everstart). The battery came with the trailer, and I will definitely be upgrading. The original Everstart died in May, and Walmart replaced it under warranty with a new battery.

Today, I did a parasitic load test and found that I have a parasitic draw of 0.46A when all of the fuses have been removed. As I understand, not terribly horrible, but it should be better. Nothing yet indicates how I can completely drain my battery so quickly. I have a Schumacher battery charger and it indicates that the battery is good. Tomorrow I am going to run load tests on the fridge, HW heater, water pump, and furnace, individually and concurrently. Once I have real numbers than I can better understand where I stand, and how to proceed.

There just is no room on the tongue for a double battery setup. The group 31 battery that Twinboat mentioned, will fit my mounting area if I purchase another box so that may be my best option. I do like the idea of converting to Lithium, and I understand that they can be mounted in the front cargo area, so that may be my winter project.

Again, Thanks everyone!

[twinboat]

Originally Posted by Marine359

By useable, I’m saying if you discharge a LA battery consistently below 50% you will in fact shorten its life cycle. If you consistently discharge to 20% you will nearly cut the life cycle in half. %.

Most batteries are killed, not cycled out. You may as well get what You can from them, before they die.

If you only use half its capacity, your replacing it without using the other half.

You also only need 1/2 as many batteries. So costs are the same, when its time to replace.

[Marine359]

Originally Posted by twinboat

Most batteries are killed, not cycled out. You may as well get what You can from them, before they die.

If you only use half its capacity, your replacing it without using the other half.

You also only need 1/2 as many batteries. So costs are the same, when its time to replace.

Good point!