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Old 09-09-2021, 03:20 PM   #1
2 Rivet Member
2018 Interstate Grand Tour Ext
Bellingham , WA
Join Date: Oct 2018
Posts: 39
Question upgrade from 4 12V AGM to ? 6v AGM or ? Lithium

I am trying to decide on which Battery and Charging system I should upgrade to in order to achieve significantly*better off-grid battery life/performance, i.e. being able to run my refrigerator, water pump, TV , miscellaneous (LED) lights , USB charging iphones and the like for 2-3 days without having to use the Generator/Engine in shady / no Sun environments, and 4-5 days when in full sun (desert ).*

Here is what I currently*have in my*2018 Interstate GT:
4 12 V AGM batteries ( upgraded within the first 2 month of ownership from 2 to 4 batteries after I noticed that my 2 batteries only lasted a day or two. Initially I saw some improvement, but within the last 6 month is has degraded so bad - I can't even make it thru 24 hours without having to restart the engine or run the compressor/

3 x 100W Solar panels

Atkinson Sunexplorer 25AMP Charge Controller & Display Kit ( PVCM250D & SEDM4-LC

Magnum Energy 1000W Inverter / Charger with 20AMP AC transfer capability and a 50-AMP 4 stage Power Factor Correction (PFC) charger - Model MMS1012 and Magnum ME-MR remote control.

5.0 CU FT Nova Kool Refrigerator*w 1.6 CuFT Freezer Drawer - Model RFU7300D - rated power consumption 3.5 A per compressor

What I am contemplating:
Option 1 - 6v AGM

2 or 4 (???) 6 V AGMs - either Interstate Group GC2 - GC2-ECL-UTL RC 447 Weight 62 Ibs or GC2-HCL-UTL* RC 383 Weight 58Ibs or FullRiver DC224-6 RC 441 Weight 67.9 IBS* ( THe Fullriver cost almost twice as much as the interstate- is there justification for that? Would 2 6v be enough or should I go with 4 ?

Victron Solar Charger (which model???)* because**I suspect that my Atkinson Sunexplorer* Charge controller* (PVCM25D) stopped working. I say suspect as I have no idea nor means to actually troubleshoot it. The matching Display Kit (SEDM4-LC) does not show any information but is backlit

3000 W Inverter/Converter???

Option 2 - 12v Lithium LiFEPO4

2 Battle Born or 4 ? 100Ah 12V GC2 LiFePO4 Heated Battery Kit*(seems to fit better into the existing trays underneath the Sprinter) or 100 Ah 12V LiFePO4 Deep Cycle Battery or 270 AH* GC3 (would have to go inside)

Victron Solar Charger (which model???)

3000 W Inverter/Converter ???

Other ??*

Thank you very much in advance

PS: I am not a DIY guy, so I am also soliciting capable installers in WA, preferable WEST WA
romanf17 is offline   Reply With Quote
Old 09-09-2021, 03:47 PM   #2
Half a Rivet Short
2017 30' Classic
2022 Interstate 24X
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 15,647

I'm assuming that you are after a significant improvement in your "days off grid". You suggest at the top of your post that you are after a roughly 2X improvement.

Going to 6V AGM's from same sized 12V AGM's is kinda sorta a 10% capacity increase. If you have two 6V / 220AH batteries in series the result is 220AH at 12V. If you have two 100AH 12V batteries in parallel the result is 200AH. Both of thees are "total capacity" numbers. Usable capacity is roughly half those. ( so 100 vs 110 AH). Sure, it's more, but not a lot more.

Going from 4 AGM's at 12V to 4 AGM's at 6V takes you from roughly 200AH usable to 220AH usable. To double your capacity with AGM's you would need to go from the 4 batteries you have to 8 batteries. That's a lot of weight and a lot of space taken up.

Going to the same sized (but 1/3 the weight) Lithiums, gets you 200 usable amp hours of battery vs 2 AGM's at 100AH. If you now have 4 batteries in the van, you could could go to 4 lithiums. That gets you up to 400AH usable capacity which is 2X what you have now.

So, practically the only way to significantly improve battery capacity is to go to 4 or more lithiums. If weight more than space is the limit, you could go to quite a few lithiums.

Regardless of what batteries you go with, the Victron will do a better job on solar than what you have. It *might* add 10% to your total capacity. They are sized by the output current you expect so something in the 35 A range or larger would be the target.

Going to a 3KW inverter simply makes things worse. More load means less "battery time".

If you are going to a pro to have this all done, AM Solar is up in your neck of the woods. They are one of the best in the nation at doing this. It's worth the drive to get to them. Rather than tell them every detail of this or that, I'd let them make the fiddly little decisions. Things like "which Victron" or "which switch here" or "what to do about the converter/charger" is the kind of stuff you are paying them to know.

Cost wise, the AGM's are very expensive for the usable capacity you get. Lithium's have become the "go to" choice. The only other alternative would be "on sale at Costco" flooded cells.

uncle_bob is offline   Reply With Quote
Old 01-16-2022, 03:54 PM   #3
2 Rivet Member
2018 Interstate Grand Tour Ext
Bellingham , WA
Join Date: Oct 2018
Posts: 39
upgraded from 4 AGM to 4 Lithium

First of - thank you again Bob for your great advise. I contacted AM Solar but because of timing and logistic, I used our local installer to do the upgrade to Lithium. Here is my new setup:

1) 4 Battle Born 100 AH 12V GC2 LifePO4 Heated Batteries

2) Victron SmartSolar MPPT 100/30 & 100/50 charge controller

Initial Observation

The Victron Charge Controller definitely made a difference. It charges the batteries nicely (when Sun is available of course)

The batteries last longer but the alternator is not charging the batteries (For some reason my installer did not think that a DC-DC charger is required as recommended by many).

I contacted BattleBorn and they also recommended I install the Victron Orion-TR Smart 12/12V-30A Isolated Charger

2018 AS Interstate GT
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