LiFePo4: (2)-100Wh or (1)-206Wh?

[Theo-FRF]

While our (2) series-connected FLA GC2 6V 208Ah batteries have been outstanding performers, we are thinking of replacing them with 200Ah of a LiFePo4 alternative. SOK make both a 100Ah and a 206Ah battery. For maximum charging, we'll need to replace the converter connected to our WFCO 8955 power system. We'll also be moving the battery(s) location from the tongue to under the dinette seat so that means I'm also prepared to make some wiring changes.

My question has to do with the pros & cons of purchasing a single 200Ah battery versus two 100Ah batteries connected in parallel. I seem to remember that there was a difference in the effective maximum discharge rate (100W vs. 150W) or, perhaps, it was the maximum charge current. I realize that two 100Ah batteries will also provide limited backup should one battery fail, but are there other considerations that my limited septuagenarian intellectual powers prevent me from understanding?

Many thanks in advance!

P.S. I will eventually be building a solar suitcase to help charge the battery(s) during dry-camping/boondocking. However, I'm doing this in stages and want to execute the LiFePo4 change first to collect charging data (shore and genny) to feed into solar suitcase specs. That, and I can't afford to do BOTH this coming year!

 

[TitanMike]

The answer whether or not to use TWO 100 ah batteries rather than one 200+ Ah battery will depend on the BMS in the 200+ Ah battery.

If all one wants to do with the batteries is run the lights, water pump, furnace, and provide 12 v the other small power draw items, then it really makes no difference. Either will work.

If however you want to use a large Inverter to power a microwave, etc, then the BMS in the 200+ ah battery gets to call the shots.

A microwave will typically cause the inverter to draw in excess of 125 amps (using my inverter/microwave as an example) which may exceed the capacity of the large battery's BMS. A 100 ah battery will typically have a BMS that will deliver up to 1 C discharge rate (100 amps) and two in parallel will deliver 200 amps with no issues.

Many 200+ ah batteries will only deliver 100 amp continuous discharge although some may have 150 amp capabiliy. The 200+ ah battery may not be able to meet the current needs of a large Inverter (2Kw-3Kw) that is needed for high draw items like a microwave, especially when the inrush current is considered.

Again, no large inverter to run a microwave, etc, Either will work just fine.

If a large Inverter enter the picture then a pair of 100 ah batteries is best. Then again, one could use TWO 200+ Ah batteries, not only covering the high current, but having more power available at the same time.



Those are my thoughts.

 

[corn18]

While our (2) series-connected FLA GC2 6V 208Ah batteries have been outstanding performers, we are thinking of replacing them with 200Ah of a LiFePo4 alternative. SOK make both a 100Ah and a 206Ah battery. For maximum charging, we'll need to replace the converter connected to our WFCO 8955 power system. We'll also be moving the battery(s) location from the tongue to under the dinette seat so that means I'm also prepared to make some wiring changes.

My question has to do with the pros & cons of purchasing a single 200Ah battery versus two 100Ah batteries connected in parallel. I seem to remember that there was a difference in the effective maximum discharge rate (100W vs. 150W) or, perhaps, it was the maximum charge current. I realize that two 100Ah batteries will also provide limited backup should one battery fail, but are there other considerations that my limited septuagenarian intellectual powers prevent me from understanding?

Many thanks in advance!

P.S. I will eventually be building a solar suitcase to help charge the battery(s) during dry-camping/boondocking. However, I'm doing this in stages and want to execute the LiFePo4 change first to collect charging data (shore and genny) to feed into solar suitcase specs. That, and I can't afford to do BOTH this coming year!

Will you be running an inverter?

If not, six one way half dozen the other. There isn't anything that I know of that draws more than 15A on the DC only side of my 5er.

If so, you will need amps. One SOK battery is rated for 100A discharge which will give you about 1,000W output from an inverter. Two SOK batteries will give you 2x100A = 200A which will be good for 2000W output from an inverter.

I know for certain that my SOK batteries will output 143A each and SOK even says they are good for 150A.

Charging is rated 50A/battery. If you get a giant charger, that would be a problem with one battery. My 120A charger can push the full 120A into my 2 SOK batteries, so there must be some headroom on the SOK BMS above the 50A limit.

If you have no inverter, I would get 2x100Ah. If you plan on inverting, you must get 2xSOK batteries but I would get 2x206Ah because that's what I did.

 

[Theo-FRF]

Thank you both for the very fast replies!

When dry-camping/boondocking, we only use (2) 300W inverters: one for the TV (maybe 3-hrs/day) and one for the powered theater seats (momentarily to adjust). We never use the microwave unless we're on shore power.

However, for future considerations, we may want to go to (2) 100Ah batteries in case we upgrade the TT and find ourselves needing to power a 2-3000W inverter.

Thanks a 10^6!

 

[TitanMike]

Thank you both for the very fast replies!

When dry-camping/boondocking, we only use (2) 300W inverters: one for the TV (maybe 3-hrs/day) and one for the powered theater seats (momentarily to adjust). We never use the microwave unless we're on shore power.

However, for future considerations, we may want to go to (2) 100Ah batteries in case we upgrade the TT and find ourselves needing to power a 2-3000W inverter.

Thanks a 10^6!

Looking to the future is pretty much standard in my planning for an upgrade. I hate having to "pay twice".

There was a time I thought I'd never use the microwave off battery power. That is until I upgraded to a 2Kw Inverter and now it seems like I use it daily when off grid.

Good luck.

 

[sdelam]

I went with two 100AH more for redundancy than anything else. I have a 1200w inverter and do not use it for the microwave. However I do power all my other 120v outlets with it. I did a test to see max use by turning on all lights, fans, radio, TVs, and a small coffee pot. Max draw was around 88-89 amps. Normal draw from one TV and a light/fan is closer to 5-6 amps.

 

[CHICKDOE]

Another large amp draw would be a built in generator. It doesn’t sound like this applies to this case but I mention it as I have read some posts where a person upgraded to lithium and was then unable to start his generator.

 

[Tom48]

The thing to watch is the continuous amperage rating of the battery and that will be controlled by the BMS.

I saw some good deals on 200 amp batteries because they only had a 100 amp BMS in them. Iceman saw some good deals on 100 amp batteries because they had a maximum continuous rating of 1/2 C or 50 amps. I looked at chin 200 amp batteries that had two prices and discovered that was the difference between a 100 amp BMS or a 200 amp BMS in the same box with the same amperage rating. If you hope to run microwave for a couple mins here and there, 200 amps will be enough, but at min you will need a 200 BMS or two 100 amp BMSs in parallel

 

[dustman_stx]

You could go with a BattleBorn GC3 at 270AH and have 300A continuous capability. As others have alluded, the cheaper the battery the cheaper the BMS typically.

 

[Theo-FRF]

You could go with a BattleBorn GC3 at 270AH and have 300A continuous capability. As others have alluded, the cheaper the battery the cheaper the BMS typically.

Impressive specs on this. However, this may be overkill for our current and future needs. Also, $2360 is way out of our budget! I still need to fund the DIY solar suitcase project.

 

[mnoland30]

What is it about your current batteries that you are dissatisfied with? I love lithium batteries, but just can't see the need at that price point. My two GC batteries and 200 watts of solar do everything I need. Of course I don't use the microwave (we needed the storage space), and don't run the heater after bedtime.

 

[Theo-FRF]

What is it about your current batteries that you are dissatisfied with?...{snip}

Well, first of all, the GC2s have been a terrific value for <$200! I do take very good care of them and maintain/monitor them regularly. Being FLA, however, we can only get ~100Ah of safe usage out of their total 208Ah capacity.

Over the last three years we've found ourselves dry-camping or boon-docking 80-90% of the time as most of the beautiful state parks in the Northeast do not have electrical hook-ups. We have a genny, but it takes a while (~6hrs) to charge up our FLAs with the Honda 2200i after a day's use (no microwave/no aircon).

Additionally, our (2) GC2s add about 130lbs to the tongue weight of the TT and, with the 23IKSS being one of the heavier Roos, we'd like to pare-down its weight a little. Moving the batteries inside to just over the axles is also something we'd like to do. So, after we complete the funding of our "Lithium Project Budget" at the end of December, we want to move ahead with our project.

The advantages to us are:

1. About twice the usable amp-hours resulting in a stay of 6-days without charging instead of 3-days;
2. A decrease in the charging time (to replenish our usage);
3. A 2/3 reduction in battery weight;
4. The ability to better locate the battery weight;
5. No maintenance.

The follow-on project will be to build a 200W Solar Suitcase to further reduce the need to recharge the battery(s) via internal combustion. Unlike New Mexico, the Northeast is not the best area for solar charging so I doubt that we will ever be able to camp without bringing the genny, however.

 

[lcangler]

I am also doing the same change, moving to 2-100ah SOK batteries and moving battery location from the tongue to the back of my camper under the jack knife sofa. Currently the converter is in the very back of the camper 25' from my lead acid battery. My question is, how did you handle your electric jack if you had one? Mine is just hooked directly to the battery up front. When I move my new batteries inside and to the back, the jack won't have power unless I make a very long run of 6 guage wire (30amp draw). What did you end up doing?

 

[CHICKDOE]

if your converter is at the rear and the batteries are on the tongue there has to be some cables between the two. how if you move you batteries to the rear can you install a new short cable between them and the converter and reuse the existing cables from rear to the tongue to power the jack?

 

[dustman_stx]

I am also doing the same change, moving to 2-100ah SOK batteries and moving battery location from the tongue to the back of my camper under the jack knife sofa. Currently the converter is in the very back of the camper 25' from my lead acid battery. My question is, how did you handle your electric jack if you had one? Mine is just hooked directly to the battery up front. When I move my new batteries inside and to the back, the jack won't have power unless I make a very long run of 6 guage wire (30amp draw). What did you end up doing?

You already have a run of wire going from the battery to the power center- just use that for your tongue jack. You’ll have to install a new run from the new battery location to the power center anyway.

 

[dustman_stx]

Looks like I was 4 minutes slow on my reply

 

[doanshop]

Just like flying

If you are flying and you have only one engine and it dies you stop flying and crash if you have two engines, you can keep going and get to safety. just my way of thinking. I had one of my FLA batteries go bad isolated it and continued to camp on just the one instead of having to go buy a battery somewhere to finish camp trip. With FLA you can get them anywhere but Lithium not so easy right now. That happened before I went to Lithium so far, I haven't had a Lithium go bad yet 3 years on first set that I pulled from camper to use on trolling motor and replaced with Chinns with Blue tooth two 100amp

 

[Theo-FRF]

We've changed our battery plans since January. We'll still replace the older GC2s with LiFePo4s in our TT, but we've scaled-back the project. The change was driven by our decision to buy a used MH in 2024/25. This has resulted in our keeping the new batteries on the TT's a-frame and enclosing them in a more secure compartment.

The idea here is to purchase a set of batteries that will fit directly into the future MH. When it comes time to sell the TT, we'll replace the new lithiums with the original GC2s and move the lithiums over to the MH. However, we need to measure the battery compartment in our planned new-to-us MH in order to decide whether we go with (2) 100Ah batteries or (if the budget allows) (2) 200Ah batteries. In either case, each battery's max discharge rate is 100Ah so we should have the headroom to support the MH's increased draw.

As a pilot, I certainly appreciate redundant systems!

 

[RhumbleFish]

I'm a big fan of the Chins product, Theo, and Will Prowse backs it up.

For additional headroom, how about (1) 300Ah smart battery, with low temp shutoff protection and integrated heaters for extra cold days? (ramp down your amp hours to reduce cost).

With the new blutooth monitoring through the upgraded BMS, these are an absolute killer deal.

 

[Theo-FRF]

{snip}...What did you end up doing?

We postponed and reduced the scope of our project, but the plan was to move the battery cut-off switch to the new battery location and run a couple of 8AWG wires to the jack and the chassis-mounted circuit breakers. Of course, we'd plan to run new 2/0AWG wires from the new lithium charger/coverter to the batteries.