Battery Gurus

[TwoKozy]

I have read so much information about what type of batteries to invest in, I'm confused.....We have a 2020 Rockwood 2511S. have travelled from Las Vegas to Bar Harbor Maine in 3 months. We bought our Mini Lite slightly (never) used(long story).We have been doing campground RVing, with minimal E&W hookups. Couple of nights in Casino/restaurant parking lots.
See attached the two batteries that came with our TT. Notice they never punched out the date.


The one with the negative cable has two cells that I fill up(not top off)monthly.
The other 22 cells need an occasional top off. All with distilled water.I even purchased some electrolyte to put in those two cells and it didn't last a month.
How long can we survive with 22 battery cells fully functional.
Can I replace just one of the batteries or do them as a set?
Should I get a deep cell sealed type battery? Any suggestions of manufacturers?
Don't believe my stock inverter (charger) would be able to charge a lithium type battery, so I don't want to go that route yet. Or would it?
No we do not have a battery monitoring system. And no solar.
Any positive feed back or suggestion will be appreciated.

[18LT]

The general consensus is to replace both. If you've been happy with these batteries, buy two of the same. If you'd like to have longer offgrid periods, buy two 6-volt golf cart batteries and connect them in series.
I've replaced only one of two, knowing the other one would probably fail in the not-too-distant future, and almost always near the end of the camping season.

[njfishing]

Batteries wired in parallel will always settle to the lowest common denominator so if one is bad it will drain the other. If you want to get the most out of what’s left of the good battery use it stand alone. If you’re going to replace them both, another vote with going with two 6 volt
Golf cart batteries.

[flyflotrtim]

Good advice above. replace both batteries at the same time. Your batteries are the common RV sellers installs. Go 6 volt Golf Cart if you plan to do much boondocking. Costco and Walmart get frequent nods for best prices on the 6volts. A portable 100 + watt solar system would be very helpful down the line.

[TwoKozy]

flyflotrtim,
Don't follow how two 6volt in series will out last two 12v in parallel. Would like the ability or option to boondocks for two or three nights.
Is the 100w solar panels all the Forest River Rockwood 2511S pre wired (no controller)solar ready wiring will handle or all we would need to replenish two 6 volt dc batteries?
Thanks

[rsdata]

Originally Posted by Two Koczeras

flyflotrtim,
Don't follow how two 6volt in series will out last two 12v in parallel. Would like the ability or option to boondocks for two or three nights.
Is the 100w solar panels all the Forest River Rockwood 2511S pre wired (no controller)solar ready wiring will handle or all we would need to replenish two 6 volt dc batteries?
Thanks

you have the minimum battery size a group 24... typically get 50% of the Ah rating so yours are 81 Ah times 2 in parallel ( 162Ah) so you can expect 81 Ah from your current batteries PLUS if one is bad the other CANNOT make up for that loss of power.

An Interstate GC2 battery is physically larger and 225 Ah @ 6 volts so two in parallel is 225 Ah at 12 volts and 50% discharge ( fully discharged) is 112.5 Ah of power... about 40% more power available to use and nothing needs to change with your Converter/charger.

[18LT]

Originally Posted by Two Koczeras

flyflotrtim,
Don't follow how two 6volt in series will out last two 12v in parallel. Would like the ability or option to boondocks for two or three nights.
Is the 100w solar panels all the Forest River Rockwood 2511S pre wired (no controller)solar ready wiring will handle or all we would need to replenish two 6 volt dc batteries?
Thanks

Actually, your old Interstate FLA batteries were pretty good for deep cycle use. Doing the reserve capacity-to-amp hour conversion, your batteries had a combined amp-hour capacity of 116 amp hours (each of your batteries had a reserve capacity of 140 minutes for a total of 280 minutes of reserve capacity, which converts to 116 amp hours). A pair of 225 amp hour Trojan T-105 6 volt golf cart batteries wired in series for 12 volts would give you 225 amp hours. So the two golf cart batteries will provide 109 more amp hours than the two Interstate batteries
Trojan offers a T-125 6 volt golf cart battery with 240 amp hours. It's my option the a set of the T-125 batteries would work well for a few nights off the grid.
I don't have any association with Interstate or Trojan. It's just that they're both well known brands.
It's late and I'm already half asleep so if I made any mistakes, feel free to let me know tomorrow.
I'm using the reserve minutes to amp hours calculation of reserve capacity divided by 2.4; 140/2.4=58.3 X 2=116.6 amp hours.

[flyflotrtim]

Originally Posted by Two Koczeras

flyflotrtim,
Don't follow how two 6volt in series will out last two 12v in parallel. Would like the ability or option to boondocks for two or three nights.
Is the 100w solar panels all the Forest River Rockwood 2511S pre wired (no controller)solar ready wiring will handle or all we would need to replenish two 6 volt dc batteries?
Thanks

RSDATA answered your question re 2 6V batteries. Your TT can "handle" all the solar input you want to give it. I suggested a 100 watt panel because I find that on a sunny day it will come close to replenishing what I use if I am extremely careful with my usage. (no heater fan, tv, etc) The portable panels are simple and come with a controller, all you need to do is plug them in to your batteries. A 200 watt portable panel is not a lot more expensive than the 100 Watt but I felt it was a bit heavy for me to transport and move around each day. Folks who camp for extended periods and/or stay in one location for extended periods of time often mount solar panels to their roofs and/or build lazy susan type mounts to rotate the portable panels throughout the day to follow the sun. My camping is frequent but rarely exceeds ten days so I try to keep is simple.

[rsdata]

Actually, your old Interstate FLA batteries were pretty good for deep cycle use. Doing the reserve capacity-to-amp hour conversion, your batteries had a combined amp-hour capacity of 116 amp hours (each of your batteries had a reserve capacity of 140 minutes for a total of 280 minutes of reserve capacity, which converts to 116 amp hours).

without doing any conversions just look up the specs for SRM-24 Interstate battery...

https://www.interstatebatteries.com/products/SRM-24

Specifications
Part NumberSRM-24
Group Size24M
Cold Cranking Amps (CCA)550
Cranking Amps (CA)690
Reserve Capacity (RC)140 minutes
Amp Hours (Ah)81

[TwoKozy]

Thanks to all. Sounds like it's time to price and size out (will they fit in my CAMCO dual battery box?) some 6v golf cart batteries.
Maybe invest in some portable solar panels?
Or is a battery monitoring system more advantageous at this point?
Thanks for all your quick responses. You are truly helping this 67 yr old newbie feel more confident as a traveller and camper.

[18LT]

A state of charge meter is nice to have. If you decide to buy one, make sure it has a correction factor for the self-discharge rate of lead-acid batteries. My inexpensive Qwork meter does not, but I have lithium batteries, which have an extremely low self discharge rate.
The Bluetooth ones that use a cellphone app (Victron comes to mind) seem to be popular.

[njfishing]

Originally Posted by rsdata

you have the minimum battery size a group 24... typically get 50% of the Ah rating so yours are 81 Ah times 2 in parallel ( 162Ah) so you can expect 81 Ah from your current batteries PLUS if one is bad the other CANNOT make up for that loss of power.

An Interstate GC2 battery is physically larger and 225 Ah @ 6 volts so two in parallel is 225 Ah at 12 volts and 50% discharge ( fully discharged) is 112.5 Ah of power... about 40% more power available to use and nothing needs to change with your Converter/charger.

Exactly and based on my experience with two 6 volts, if you run your fridge on propane, don't use your heat or TV and use your lights and water pump sparingly, you should be able to make 2 nights and if really careful 3. If however you don't have a propane fridge and or you run your heat, you'll likely need to charge your batteries each day and 100 watts of solar is not going to be enough to do that. You'll need a generator and it will have to run at least 3 hours to get you back up to a full charge.

Most frequent boon dockers who rely on solar and run two 6 volts are typically using 400 watts of solar or more, depending on what they want to run. The more serious ones also have a generator as a back up just in case there's no sun.

[18LT]

Well gosh, the Interstate website certainly does say the the OP's Interstate batteries had 81 amp hours. So please disregard my use of an internet calculator.
As mentioned in one of the posts, the guideline for discharging lead-acid batteries is to try to limit the discharge to 50% in order to prolong battery life and reduce the time necessary to recharge. Can you go deeper? Sure. The deeper the discharge, the longer it takes to recharge the battery and the battery life is shortened.
One of the big selling points of lithium iron phosphate batteries is their much quicker recharge times, assuming a lifepo4 charger is installed. Another selling point is the lifepo4 battery's ability to maintain a constant voltage for about 95% of it's rated capacity, while a lead acid battery's voltage will drop during discharge.
Are lithium iron phosphate batteries the answer? I don't know. I guess it depends on how much money you want to spend on the batteries, charger upgrade and possibly a solar charge system, balanced against how long you'd like to be off-grid. Along with that, it helps to be aware of the downsides of lithium batteries, like they cannot be charged if the battery temperature is below 32 degrees F. High quality lifepo4 batteries have a low-temp disconnect but lower priced ones do not. So buyer beware.
All of that being said, I'm having a great deal of fun with my lifepo4 batteries and solar charge system. But I've spent a lot of money on it, especially the batteries. My camper's 12-volt fridge, the furnace and other electrical devices use about 75 amp hours during the night. With a total lifepo4 battery capacity of 500 amp hours, and with 380 watts of panels on the roof, we could be unplugged for several days before using the generator. I have two more 190-watt panels in the garage, ready to be mounted on the roof. As I mentioned, I've spent a couple of bucks but I'm having fun with this.
So in my opinion, the easiest and most cost effective solution to your question is to buy the same batteries as you have or to buy golf cart batteries, along with buying a nice quiet inverter-generator to provide "house" power during a few daylight hours and to recharge your new batteries.
Also, buy a battery hydrometer, along with some appropriate personal protective gear, and read up on how to use it to determine your batteries' state of charge.
But I ran wood through a machine for 30 years, so my opinion is probably worth what you paid for it.
On a completely unrelated topic, I wonder how much I'd need to spend on an ad, selling my opinions. There sure are a lot of ads on this forum. And yup, I understand the financial dynamics of operating an ad-based forum vs asking users to buy a membership (which is usually the kiss of death for a forum). Still, I wonder if anyone would pay me for all the meaningless garbage that's in what's left of my brain. Yeah, probably not.