Cell charge voltage is only one aspect.
What type of BMS balancing does it have. How fast does it work, is it active or passive. How much time does it need to do its job among other things is all happening that few companies bother to tell us about or even know if you ask them. Let alone have data you can see or check as to what’s going on in that black box.
So in regards to say fortress, maybe they changed their Bms and therefore their charging parameters to better fit the new unit.
I know eg4 just changed to an active balancing which they say is better than passive. But most have passive as far as I know.
Simpliphi is sort of an orphan at this point being the only one using cylindrical cells if I’ve got the data right. Or companies like battleborn. ( given the horrific press they are getting on the web it’ll be interesting to see if they stay in biz)
It’s still a very fast moving field and hard to stay up on it all.
We're not the only ones wondering about best settings for LFPs.
I've noticed over the years both Simpliphi and Fortress have
changed their recommended charge settings substantially. Fortress
seems to have gone to a higher voltage and very low absorb time.
Considering they're roughly the same cells inside on all of these,
I find the variations in settings interesting.
Beware, some batteries like the Simpliphi will literally let the
smoke out if they go over 60 v. I was excited about the 15 cell
(48 v nominal) HomeGrid batteries, since they would be closer to
lead acid voltages. However, we ended up having quite a bit of
firmware troubles, and the "outdoor" enclosure and heating left a
lot to be desired.
Like William, I don't consider myself quite an expert on LFP,
but I've done systems with Blue Planet, LiFe Blue, Simpliphi,
Fortress, Homegrid, and Midnite. Even though I had a hard time
finding charge settings, the Midnite Powerflo 16 has been my
favorite so far. I just did a system with a Rosie and a pair of
Powerflo s. Every possible load on in the house, then kicked the
well pump, and it didn't even blink the LED lights.
Ray Walters
Remote Solar
On 1/26/2026 9:51 AM, Maverick Brown
via RE-wrenches wrote:
I have never believed any LFP battery maker that has 58.4V for
charge voltage. That’s 3.65 Volts per cell in a 16S configuration.
If you have any cell imbalance inside the pack, one cell could go
above the upper limit of 3.65Vpc.
I have installed serval brands of LFP batteries, some great
brands and some not as great.
In pretty much all cases, I used 3.45Vpc (55.2V) as the
Absorb and then set other voltages as appropriate based on that.
In several cases, I also enabled EQ and set it to 3.5Vpc (56)
just to make sure that cell balancing has a chance. If the
voltage is too low, you will see a wider battery to battery SOC
spread. I have corrected that by increasing the Absorb time
and/or bump up the ABS Voltage.
Many battery companies have been integration guides for their
battery to Outback or Scheider. I have digested this to see what
the ranges are for open charging. It would be good to get more
details about:
Cell balancing activation voltage
Method for reading the cell voltages internal to batteries
(a few companies have simple cables and easy apps for such,
Pytes and Fortress)
Method for reading individual battery SOC (Pytes has a
serial cable and an app; Fortress has Guardian comm box, and
there are others)
It would be good for long term health and understanding for
wrenches to have more information…
Here is my current working document on charging open loop.
Let me know what you would do differently. Any suggestions are
appreciated. I will send the XLS version to anyone who wants
it.
Maverick
Brown
Off-Grid Solar Commander since 2006
Maverick Solar Enterprises, Inc.
•
Solar Commander Remote Power
The specs for this particular battery list a
charging voltage up to 58.4V. I believe the BMS
protection level is set at 60V, but I need to
confirm with the manufacturer when they open on
Monday.
I just noticed that the AIOs responded
to a relatively high load and entered a re-bulk type
of behavior. But the voltage stayed withing an
acceptable range. I'm not clear on how the AIO
handles re-bulk and also why the float voltage
setpoint isn't being respected (or how absorb time
is determined).
Jason Szumlanski
Principal
Solar Designer | Florida Solar Design Group
NABCEP
Certified Solar Professional (PVIP)
Florida
State Certified Solar Contractor CVC56956
Florida
Certified Electrical Contractor EC13013208
On Sun, Jan 25,
2026, 12:48 PM Zeke Yewdall via RE-wrenches < [email protected]>
wrote:
I see on the Lithionics spec sheet it says a
charged voltage of 57.6 volts This seems very
high for a 16 cell LFP battery. I am used to
using 55 to 56 volts, maybe 56.5 volts at most
on a 16 cell LFP. I suspect that the 57.6 is
the protection voltage of the BMS, not the
appropriate absorb voltage setting. I have seen
this error a lot on lithium battery spec sheets,
where they give the overvoltage protection
level, which is not an appropriate absorb
setting for typical solar equipment.
Not everyone will agree with me, but the way
I set up absorb voltages when doing open loop
lithium battery systems is to NEVER let the BMS
do anything. if the BMS shuts off charging,
that means that I already failed... the charge
controller or inverter should have stopped
charging before the BMS feels the need to
protect the cells. Same with low voltage
disconnect... if the BMS shuts off due to low
voltage, I already failed -- I should have shut
the load off before the BMS felt the need to
turn of discharge to protect the cells. The BMS
is like an airbag...only to react in cases of
emergency when the rest of the system doesn't
work properly.
Open loop equipment (all of the traditional
outback/magnum/schneider, etc stuff, plus any
AIO's in open loop setup) is designed to always
have a battery in the system to stabilize the DC
bus voltage. Without the stabilizing effect of
the battery, voltage spikes can occur. I find
that many charge controllers, especially the
midnite classic and victron ones, can actually
keep the system fairly stable without batteries,
but charging from inverters is more
questionable, and especially charging from any
DC generators can cause severe spikes if the
battery disconnects. I have fried equipment when
a lithium battery disconnected from a large
kohler DC generator and the generator couldn't
react fast enough to keep it from spiking to 75
volts or more. This is why you never want the
BMS to disconnect... which means setting absorb
at a level where the BMS never feels
threatened. Lithium battery manufactures giving
the voltage at which the BMS disconnects as the
"charge to" voltage does not help the
situation. That may work when charging it with
a dedicated lithium battery charger, without
anything else connected to the battery while
it's charging. But in a functioning solar
system with charging from multiple sources and
loads all occurring at the same time, we need to
be smarter than the battery, IMO.
Zeke
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