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Old 11-04-2021, 08:50 PM   #21
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That was my intention,use a lithium capable charger maintainer. This was also the reasoning behind disabling the the converter charging side so both were not trying to charge the battery. My belief was they would fight each other as they tried or thought they were at capacity.
That is a long held myth by those that don't really understand electricity and how chargers work.

The smaller charger won't have enough power output to shut down the larger charger as the battery will be sucking down the voltage on both outputs. Each will operate at it's maximum output until the voltage on the battery reaches full charge. In the situation we're discussing the converter will drop to the absorption voltage it's programmed for and the small charger will continue on to the max voltage of the Lithiums.

I think the "myth" is a holdover from the days when one could control the output of the battery chargers and it was possible to crank them up to battery damaging voltage/current levels. Today's chargers built into converters and battery maintainer/chargers are a lot smarter.
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Old 11-05-2021, 05:53 PM   #22
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LiFePO - one large or two small batteries

I'm studying as much as I can on solar power, LiFePo batteries and inverters before we take delivery of the TT in Mar/Apr. One consideration was whether the setup should be a single large LiFePO battery (200+ah) or two smaller batteries in parallel (ie 100aH each). A single, larger battery will cost less than two smaller batteries, but that is not the only factor to consider.

The internal BMS of either size battery will likely have a max discharge limit of 100a. This seems to be the most common size BMS used unless one builds their own battery. If the TT has a 1000w inverter, either battery setup above will be sufficient.

However, if wanting to feed a 1500w or 2000w inverter, the 100a BMS on the single large battery will not allow enough current to pass to realize the full 1500w output of the inverter. It will be limited at ~1200w (without considering loss factors). Using two smaller batteries in parallel, each with a 100a BMS, will allow a total of 200a of current output, enough to satisfy a 2400w inverter (again, without considering loss factors).

If I've missed something here, I'd appreciate someone correcting what I missed. Maybe this should have been in a separate thread?
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Old 11-05-2021, 06:11 PM   #23
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Originally Posted by JimM2109S View Post
I'm studying as much as I can on solar power, LiFePo batteries and inverters before we take delivery of the TT in Mar/Apr. One consideration was whether the setup should be a single large LiFePO battery (200+ah) or two smaller batteries in parallel (ie 100aH each). A single, larger battery will cost less than two smaller batteries, but that is not the only factor to consider.

The internal BMS of either size battery will likely have a max discharge limit of 100a. This seems to be the most common size BMS used unless one builds their own battery. If the TT has a 1000w inverter, either battery setup above will be sufficient.

However, if wanting to feed a 1500w or 2000w inverter, the 100a BMS on the single large battery will not allow enough current to pass to realize the full 1500w output of the inverter. It will be limited at ~1200w (without considering loss factors). Using two smaller batteries in parallel, each with a 100a BMS, will allow a total of 200a of current output, enough to satisfy a 2400w inverter (again, without considering loss factors).

If I've missed something here, I'd appreciate someone correcting what I missed. Maybe this should have been in a separate thread?
You are on the right track. Different manufacturers of the "Large" LiFePo4 batteries use different BMS's that have different max continuous current requirements. A Microwave will need about 125 amp continuously while running and if anything else is running at the same time (like furnace, etc) the current requirement will be >130 amp.

Whatever your choice of battery, make sure the BMS is capable of delivering continuous current of 130 amp or more.

Even though it's more expensive, two 100ah batteries will be better on that front with each being able to deliver 100 amp continuous output.

Space may well be a consideration. It may be easier for example to install two 100ah batteries in a space butted end to end than a single larger rectangular 200 ah battery. Also may be easier to install one 100 ah battery in a small corner of a storage compartment and the other in a different corner, then connected with large gauge wires.

Nice thing about the LiFePo4 batteries is that once installed they really don't need ready access in the future. A lot like a battery in your Cell Phone with no maintenance, etc, required.
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Old 11-11-2021, 10:06 PM   #24
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YouTube videos ...

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I have a 2021 Rockwood 2509s with the solar package and it came with 2 wet cell batteries in a box on the tongue. These batteries work ok, but don't last very long. I want to get some lithium batteries but I want to put them in the box on the tongue. I don't think I can fit two (or more), I'm concerned about the temperature here in Colorado, and I'm worried about theft.

I would like to put them under the couch but does anyone have experience rerouting the battery cables from the tongue to inside the camper ? Is this difficult to do?
A YouTuber recently posted a 5-part series on his experiences replacing his two flooded batteries with two lithiums ... the first part is at ...

https://youtu.be/xClCqdvabAc
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Old 11-11-2021, 10:19 PM   #25
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Hybrid system

I keep a group 27 on the tongue for brakes and backup and have my 2 lipo batteries and inverter inside to serve as house batteries for the camper. Solar panels can be switched between banks as needed. Tow vehicle charges the 27 but not the lipo bank to avoid confusing the alternator. Lipos stay at 13+ volts for most of the duty cycle. It’s nice not constantly worrying about voltage draw down. I switch off the converter or disconnect the lead battery when running the inverter but it could be a cheap but inefficient dc to ac to dc charger for the 27 if needed.
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Old 11-12-2021, 10:30 AM   #26
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Easy solution....they now have Lithium batteries with heaters so they can be in the cold temps. Then you don't need to change anything.

Happy trials.....
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Old 11-12-2021, 12:19 PM   #27
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I put my lithium batteries inside, too. I left all the wiring on the tongue as is. The wires all go to two terminal strips in the battery box. The batteries, the shunt for the battery monitor, and a new cutoff switch are inside. I ran two 12 foot 1/0 AWG battery wires up past the water pump and drilled a hole into the compartment under the bed (where your couch is). (And yes, this silly app flips the pictures all around...)
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Old 11-13-2021, 12:42 AM   #28
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Like others said a heated lithium is a good idea. I also had a welder build a strong and larger battery bay that is lockable. You will love the added and consistent power and little weight on the tongue.
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Old 11-15-2021, 10:30 AM   #29
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I have a 2021 Rockwood 2509s with the solar package and it came with 2 wet cell batteries in a box on the tongue. These batteries work ok, but don't last very long. I want to get some lithium batteries but I want to put them in the box on the tongue. I don't think I can fit two (or more), I'm concerned about the temperature here in Colorado, and I'm worried about theft.

I would like to put them under the couch but does anyone have experience rerouting the battery cables from the tongue to inside the camper ? Is this difficult to do?
It is easy to do once you commit to actually doing it. Cutting holes in a new trailer is the hardest part of the process both physically and mentally.

What I did on on a prior TT was to disconnect the battery wires at the battery and at the first junction box under the trailer body. Using a small hole saw, I drilled a hole in the corrugated material directly above the junction box and then using a flash light attempted to verify there were no obstructions between the hole and the floor of my storage compartment.

I then picked a spot in the floor of the storage compartment, drilled a hole, and routed the wires up and through and eventually connected the wires to my new battery.

That junction box had an existing connection to my converter so there were no converter issues.

Regarding converters, you can generally charge your battery from multiple sources at the same time just as you can use your battery with multiple devices at the same time. If you are concerned about using a converter and a battery charger at the same time simply switch off the converter at the breaker box.
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Old 11-15-2021, 12:12 PM   #30
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Easy solution....they now have Lithium batteries with heaters so they can be in the cold temps. Then you don't need to change anything.

Happy trials.....
The only time one needs to provide heat for LiFePo4 batteries is when charging or if discharging at temps below more than 0 F.

Just "being" in cold temps isn't a big deal. Not a lot of people camp in weather that cold and those that do would be better served to move the batteries into an area heated by the furnace. More energy efficient as electricity is not the source of the actual heat.
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Old 11-15-2021, 12:24 PM   #31
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The only time one needs to provide heat for LiFePo4 batteries is when charging or if discharging at temps below more than 0 F.

Just "being" in cold temps isn't a big deal. Not a lot of people camp in weather that cold and those that do would be better served to move the batteries into an area heated by the furnace. More energy efficient as electricity is not the source of the actual heat.
Quote from Battleborn manual. The BMS will not allow a charging current under 25°F (-3.9°C) but will continue to discharge down to -4°F (-20°C). This tells me that unless you want to go camping and freeze your arse off, the battery is not an issue at cold temperatures. The lifepo4 batteries actually function at much lower temperatures than I do!
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Old 11-15-2021, 03:27 PM   #32
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Quote from Battleborn manual. The BMS will not allow a charging current under 25°F (-3.9°C) but will continue to discharge down to -4°F (-20°C). This tells me that unless you want to go camping and freeze your arse off, the battery is not an issue at cold temperatures. The lifepo4 batteries actually function at much lower temperatures than I do!
We agree.

That said, I installed my two Battleborn's in the heated area of my trailer. Both because I do camp in freezing weather and also because I'd had two batteries stolen from my previous trailer where they were mounted on the tongue.

I now use the space the batteries used to be mounted for storing my WDH spring bars and other setup items (Wheel Chocks, Jack pads, etc).
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Old 03-20-2022, 11:33 AM   #33
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I read through this thread and there is a lot of really great information here for moving the batteries into the TT.
However my plan is simple so I have just a couple of simple questions.
I am purchasing a new aluminum battery box to replace the tongue mounted plastic box, just for security reasons.
Can I just swap out my current wet cell batteries for lithium or the LiFePo batteries?
If so, what would be the weight savings on the tongue and can I use the converter and inverter that came with my 2022 Flagstaff Microlite 22TBS?
Are the wet cell batteries and the lithium batteries the same size or will I need a special battery box?
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Old 03-20-2022, 12:31 PM   #34
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I read through this thread and there is a lot of really great information here for moving the batteries into the TT.
However my plan is simple so I have just a couple of simple questions.
I am purchasing a new aluminum battery box to replace the tongue mounted plastic box, just for security reasons.
Can I just swap out my current wet cell batteries for lithium or the LiFePo batteries?
If so, what would be the weight savings on the tongue and can I use the converter and inverter that came with my 2022 Flagstaff Microlite 22TBS?
Are the wet cell batteries and the lithium batteries the same size or will I need a special battery box?
Most Lithium batteries (100 ah size) are the same size (or darn close) as the BCI Group 27 size. Now it just depends on what size your batteries are, group 24 (common) GC-2 (common modification by owners) or group 27 (often an option from dealers).
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Old 03-20-2022, 12:39 PM   #35
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The batteries that came with our TT are group 24’s and are wet cell.
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Old 03-20-2022, 01:02 PM   #36
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Originally Posted by OldCarBum View Post
I read through this thread and there is a lot of really great information here for moving the batteries into the TT.
However my plan is simple so I have just a couple of simple questions.
I am purchasing a new aluminum battery box to replace the tongue mounted plastic box, just for security reasons.
Can I just swap out my current wet cell batteries for lithium or the LiFePo batteries?
If so, what would be the weight savings on the tongue and can I use the converter and inverter that came with my 2022 Flagstaff Microlite 22TBS?
Are the wet cell batteries and the lithium batteries the same size or will I need a special battery box?
Yes you can just swap out your wet cells for lithium (Lifepo4) batteries.
You would save half the weight of the old wet cells plus gain almost double the usable capacity for the same amp hour battery size.
Yes you can use the same converter. It will do better if it has a lithium charge mode but will charge and will not damage your lithium batteries.
This has no impact at all on your inverter.
Lithium batteries come in various sizes. Measure your box and check against the intended battery size. Some will fit fine and some won't. The aluminum boxes also come in different sizes.
I hope this helps.
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Old 03-20-2022, 01:13 PM   #37
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Originally Posted by OldCarBum View Post
I read through this thread and there is a lot of really great information here for moving the batteries into the TT.
However my plan is simple so I have just a couple of simple questions.
I am purchasing a new aluminum battery box to replace the tongue mounted plastic box, just for security reasons.
Can I just swap out my current wet cell batteries for lithium or the LiFePo batteries?
If so, what would be the weight savings on the tongue and can I use the converter and inverter that came with my 2022 Flagstaff Microlite 22TBS?
Are the wet cell batteries and the lithium batteries the same size or will I need a special battery box?
The LiFePo batteries match the footprint, but some of them are just a little bit taller. If using the plastic boxes made for them, the steel straps that are made to prevent theft must be the one made for the LiFePo batteries. TorxLift makes a nice metal box for on the tongue that is extremely secure and is made for the LiFePo batteries. Not cheap, but very good. I would have gone with this, but they are for two batteries and I was upping to three.

Our TT has an outside compartment on the right side that is at the front corner of the TT. Perfect location, Plenty of room for the batteries and the electrical upgrades we're doing with room to spare. The door's just not easy for larger than life person to work through!!

You won't regret the LiFePo batteries, they're definitely worth it! Good luck with your mods and let us know how they turn out.
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Old 03-20-2022, 04:04 PM   #38
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Thanks, I will.
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Old 03-24-2022, 12:57 PM   #39
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Lots of great info here, thanks everyone for posting! We have a 2022 Flagstaff 25FKS sitting on the dealer's lot waiting for us to pick it up. I've already had them install a second 190W panel and I have a pair of Renogy 100ah heated batteries on their way, should receive them next week. The trailer has a 2 way fridge so power use should be pretty modest. Should be good for a good bit of boondocking!
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Old 03-24-2022, 01:02 PM   #40
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Lots of great info here, thanks everyone for posting! We have a 2022 Flagstaff 25FKS sitting on the dealer's lot waiting for us to pick it up. I've already had them install a second 190W panel and I have a pair of Renogy 100ah heated batteries on their way, should receive them next week. The trailer has a 2 way fridge so power use should be pretty modest. Should be good for a good bit of boondocking!
Do you have the fridge make and model number? I thought that all Rockwood/Flagstaff models were only getting 12v only fridges now.
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