[RE-wrenches] Strange battery overvoltage issue (Midnite AIO / Lithionics Battery)

Mon Jan 26 08:51:45 PST 2026

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
 • SunFlow Systems Cathodic Protection 
maverick at mavericksolar.com
512-460-9825

> On Jan 25, 2026, at 3:48 PM, Jason Szumlanski via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
> 
> 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 <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>> 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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