[RE-wrenches] Is it OK to add EG4LL-S alongside Fortress e-Vault Classic?

[Ray Walters]

Mick,

No matter how much you want to help this guy, you already know the 
answer to this in your gut.   Maybe I'm being overly cautious here, but 
this seems to be the same as what we would tell folks trying to combine 
different sizes and ages of FLA battery: Don't do it.  He should sell 
the E vault to a neighbor, and run the new cab, or (just like with FLA) 
put in a battery selector switch, and run the system on one or the 
other, and change settings each time (ugh).  Honestly I just don't see 
it working out very well, and I could see one battery powering into a 
problem in the other battery and Really having bad things happen.

I'd give it a 10% chance it will work just fine, a 30% chance it will 
work OK, but need periodic charging on one battery or the other to sync 
them, a 40% chance it will lead to premature failure of one or both 
batteries, and a 20% that you let the smoke out of one or the other BMS 
units and/ or do cell damage. (just my educated guess, but check with me 
in 5 years and see how the dice roll worked out)

I'm sure there's some DIY folks that have done all sorts of wild mixing, 
but that still doesn't mean it's a good idea.

War stories?  I've already had so much trouble with various LiPO4, that 
I definitely don't feel like being adventurous.  I've had a Simpliphi 
bank smoke all the control boards, Home grid system shut down 
intermittently and need to be dark started every couple of months, 
Fortress evault shut down at 100% SOC because of a firmware issue and 
leave a freezer full of elk rotting.....and I definitely am not trying 
any lunatic fringe stuff.

Sincerely;

Ray Walters
Remote Solar


On 10/14/2025 4:18 PM, Mick Abraham via RE-wrenches wrote:
> Hi, Wrenchies~ I sold one E-Vault Classic cabinet to an off-gridder in 
> 2021 (18.5 kWh rated). He set it up open loop even though he's got 
> Schneider XW Pro. Now he'd like more storage and asked for a quote on 
> one EG4LL-S cabinet, fully loaded (30.7 kWh).
>
> Surely he would have to stay open loop if these two brands are 
> combined. Both brands have 16 cells in series = 51.2 nominal volts. 
> However, EG4 documentation calls for 56.2 volts Bulk & Fortress calls 
> for 54.4 volts Bulk.
>
> War stories or suggestions welcomed; thanks in advance. The Wrench 
> List is the Bomb!
>
> Mick Abraham, Proprietor
> www.abrahamsolar.com <http://www.abrahamsolar.com>
>
> Cell phone or for text messaging: 970-946-6584
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