What determines the SOC of a battery?

JohnnyB · 2026-02-16T00:55:48Z

My queston is really aimed at @transparent as he seems to be a fount of knowledge in all things electrical but I thought it my be of interest to others as well. About 6 weeks ago I had a Solis inverter installed and connected a 16kWh Fogstar battery. The Solis inverter was set up to discharge to 20% SOC with the 20% figure taken from the battery BMS. When the battery reports it is at 20%SOC the inverter stops drawing power from the battery, but that 20% changable and I have been trying lower %'s. Reading online a LiFePo4 battery cell is at about 3.1V when it is at about 20% SOC. The Fogstar battery gives voltages for 8 cells and is reporting about 13% SOC when it shows the cells around 3.1V. I have checked the overall V of the whole pack with a standard volt meter and it gives the same reading as the display on the battery. I don't want to drain the battery too low every day and degrade it quicker than necessary but I want to use as much of the battery as is sensible as well. This leaves me wondering if it is low voltage that damages the cells or a low SOC, which figure should I be paying attention too, volts or SOC or something else? Thanks.

Page 6 / 6 Prev

Energy Storage

Last Post by Batpred 2 hours ago

61 Posts

9 Users

7 Reactions

303 Views

RSS

Batpred

(@batpred)

Noble Member Member

Joined: 1 year ago

Posts: 663

20/02/2026 12:57 pm

Posted by: @upnorthandpersonal

↑

The easiest way to analyze what's going on is to post screenshots of the BMS configuration parameters and the inverter settings.

I agree.

Fogstar confirmed that the Seplos BMS does not slow the charging down, so no worries. 🙂

The HA charts will help future readers to get clarity.

Useful to have these prompts in the Forum to learn and fine tune where possible!

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

ReplyQuote

Page 6 / 6 Prev

Forum Jump:

Previous Topic

Currently viewing this topic 1 user ( JohnnyB ) .

Recently viewed by users: Transparent 37 seconds ago.

27 Forums
2,495 Topics
57.8 K Posts
223 Online
6,220 Members

Forum Icons: Forum contains no unread posts Forum contains unread posts

Topic Icons: Not Replied Replied Active Hot Sticky Unapproved Solved Private Closed

RE: Humidity, or lack thereof... is my heat pump making rooms drier?

I remember reading about this a couple of years ago, so...

By Mars , 16 minutes ago
RE: Electricity price predictions

@transparent Triggered by the various commen...

By JamesPa , 39 minutes ago
RE: Solis inverters S6-EH1P: pros and cons and battery options

Just to wrap this up here for future readers: The S...

By Batpred , 1 hour ago
RE: Struggling to get CoP above 3 with 6 kw Ecodan ASHP

Welcome to the forums.I assume that you're getting the ...

By Sheriff Fatman , 1 hour ago
RE: What determines the SOC of a battery?

I agree. Fogstar confirmed that the Seplos BMS does ...

By Batpred , 2 hours ago
RE: Say hello and introduce yourself

@editor @kev1964-irl This discussion might be best had ...

By GC61 , 3 hours ago
RE: Testing new controls/monitoring for Midea Clone ASHP

@benson — as @tasos suggests, plotting multiple variabl...

By cathodeRay , 5 hours ago
RE: Midea R32 Monobloc MHC-V12W in 1989 Detached House: Noise from Pipes/Airing Cupboard, DHW Schedule Not Always Heating – Advice Needed?

@painter26 — as @jamespa says, it's for filling and re-...

By cathodeRay , 7 hours ago
RE: Oversized 10.5kW Grant Aerona Heat Pump on Microbore Pipes and Undersized Rads

@uknick TBH if I were taking the floor up ...

By JamesPa , 17 hours ago
RE: Getting ready for export with a BESS

I would have not got it if it was that tight

By Batpred , 19 hours ago
RE: Setback savings - fact or fiction?

I also need to correct something I said by mistake earl...

By cathodeRay , 19 hours ago
RE: Need help maximising COP of 3.5kW Valiant Aerotherm heat pump

@judith thanks Judith. Confirmation appreciated. The ...

By DavidB , 22 hours ago
RE: Recommended home battery inverters + regulatory matters - help requested

That makes sense. I thought better to comment in this t...

By Batpred , 23 hours ago
Bosch CS5800i 7kW replacing Greenstar Junior 28i

My heat pump journey began a couple of years ago when I...

By Slartibartfast , 23 hours ago
RE: How to control DHW with Honeywell EvoHome on Trianco ActiveAir 5 kW ASHP

The last photo is defrost for sure (or cooling, but pre...

By JamesPa , 1 day ago
RE: Plug and play solar. Thoughts?

Essentially, this just needed legislation. In Germany t...

By Batpred , 1 day ago
RE: A Smarter Smart Controller from Homely?

@toodles Intentional opening of any warranty “can of wo...

By Papahuhu , 1 day ago
RE: Safety update; RCBOs supplying inverters or storage batteries

Thanks @transparent Thankyou for your advic...

By Bash , 1 day ago
RE: Air source heat pump roll call – what heat pump brand and model do you have?

Forum Handle: Odd_LionManufacturer: SamsungModel: Samsu...

By Odd_Lion , 1 day ago
RE: Configuring third party dongle for Ecodan local control

Well, it was mentioned before in the early pos...

By F1p , 2 days ago
RE: DIY solar upgrade - Considering adding more panels

I know this is a bit old, but it made me wonder what co...

By Batpred , 2 days ago
RE: New Vaillant aroTherm Plus in black - When will it come to the UK?

@majordennisbloodnok Daikin, take note! (In fact, I hav...

By Toodles , 2 days ago
RE: Midea ASHP – how to set weather compensation

@mk4 — good work! First, I agree, no evidence of cycl...

By cathodeRay , 2 days ago

Forums

What determines the SOC of a battery?

Join Us!

Worth Watching

Latest Posts

Members Online