Can't keep Battery SOC at the target best_soc_keep [Solis Inverter]

[Lebronic23]

Describe the bug
Battery is stuck at 14%; predBatt not allowing it to go down any further (frequent charging to keep it at 14%!)
best_soc_keep is set to 0.4KWh
Battery capacity 5kwh
Solis Inverter (S5 Hybrid)

Expected behaviour
The battery should be used all the way down to below 10% based on the set value.
Is PredBat supposed to keep topping up the battery at the expensive rate, to keep feeding the house from the battery?
It should stop charging the battery and allow the house load to be fed from the grid until the low-rate time kicks in.

Predbat version
Been like that for 2-3 months
v8.29.11

Environment details

• Solis 3.6Kw S5 hybrid inverter with 5KWH battery
• Standard HAOS installer
• Anything else?

Screenshots

Log file

27524 | 2025-12-14 21:35:06.426382: Setting charging SoC to 0% as we are not within the charge window and inverter doesn't support target SoC -- | -- 27520 | 2025-12-14 21:35:06.426267: Inverter 0 Current Target SoC is 10%, already at target 27519 | 2025-12-14 21:35:06.426239: Inverter 0 adjust target SoC for export to 0% based on requested all inverter SoC 0%

Predbat debug yaml file

predbat_debug.yaml.txt

[gcoan]

can you include a full logfile please not just a single line

what's your reason for setting best_soc_keep, are you able to leave it at zero or change best_soc_keep_weight to put less weighting on keeping that SoC level

https://springfall2008.github.io/batpred/customisation/#battery-margins-and-metrics-options

predbat can plan charging to keep your SoC above best_soc_keep, even if its at a higher rate. Reducing the weighting can reduce this behaviour

[Lebronic23]

I'd always like to keep some buffer in the battery for SOH & longevity. Solis inverter is set to overdischarge alarm @7% and will do AC charging below @5% I guess; hardly ever needed AC charging to get the battery back from that low percentage.

If soc-keep is set to 0%, we're just shifting the problem back - or maybe I need to disable AC charging, but in the winter that will switch off the inverter completely if the battery @0% quite early.

Still not sure why it's stuck at 14% instead of 8-9% that Soc_keep is set to. Also the behaviour is weird it keeps charging the battery to say 15% and then supply the house from the battery instead of the grid; rinse and repeat with the round trip losses

Previous to using PredBat, Solis inverter will stop supplying the house from the battery at a specific % and only goes into AC charging if enabled at a lower percentage or at reduced rate time.

log file
predbat.log.txt

[gcoan]

can you include the plan showing this behaviour as well please

you can use best_soc_min to set a minimum soc level for the inverter, it works slightly differently to soc_keep in that predbat will program this as the lowest point on the inverter. So set it to 7 or 8 to stop the over discharge alarm?

[Lebronic23]

Here is the planning when the SOC is around 14%, it still think that it should go down to 10% but it keep it at 14%

and here it keeps charging since it got stuck at 14% later in the afternoon today.

If soc_min is used and set to 10%, will the plan stop charging the battery to keep supplying the house and feed the house from the grid instead? just like how it operates on the solis inverter...

[gcoan]

Here is the planning when the SOC is around 14%, it still think that it should go down to 10% but it keep it at 14%

and here it keeps charging since it got stuck at 14% later in the afternoon today.

By "it" I think you are referring to Predbat, but I don't see any evidence of this.

What I see is Predbat thinks the battery will drop from 14 to 10%, that's what's in the plan and Predbat plans to leave the battery in Demand mode to let the SoC drop and remain at the 10% minimum until the cheap period.

As the battery runs out predbat plans that you will start grid importing and I see the cost increasing some time in the 21:30 slot when your battery runs out and the grid import starts.

I'm not sure what the second graph is showing, I'm guessing import power which starts from sometime around 6/7pm. There could be a number of reasons for this, your house load could be higher than your inverter can support, your inverter could be stopping discharging earlier than Predbat thinks it is, I don't know.

At the moment this looks like an inverter question and not the predbat plan that looks on the face of it fine.

[Lebronic23]

This will probably show it better.
The previous one was a bit compressed, but essentially, the battery is depleted and reaches 14% at some point in the afternoon.
Predbat plan shows SOC should go to 10% as planned but instead is doing charge bursts (3Kw) every few minutes to top up the battery to 14% and then leave the battery to supply the house (load goes back to ~400w) and then as battery SOC dips below 14% (by 1%), it kicks in a new charge burst, rinse and repeat.
There is no load demand from the house to cause this. and the battery soc will continue to be steady at 14%.

(Solax-based Solis Battery power parameter is a bit messed up as it doesn't show negative power (load) and positive (charge) it combines both in a single variable) - a picture from Solis app would be better but would be at 5min interval so wouldn't show the true frequency of those bursts.

[gcoan]

This will probably show it better.
The previous one was a bit compressed, but essentially, the battery is depleted and reaches 14% at some point in the afternoon.

Thank you, this graph is clearer.

Predbat plan shows SOC should go to 10% as planned

Agreed

but instead is doing charge bursts (3Kw) every few minutes to top up the battery to 14% and then leave the battery to supply the house (load goes back to ~400w) and then as battery SOC dips below 14% (by 1%), it kicks in a new charge burst, rinse and repeat.

This is where we disagree. "is doing charge bursts every few minutes to topup the battery"

What is, Predbat is instructing the inverter to do this?
The inverter is doing this on its own?
What is?

I'm sorry if this comes over wrong but I do not have a Solis inverter, I don't know how it works, but I have a reasonable idea how Predbat works and what you are supplying so far doesn't help get to the bottom of the problem.

At the moment you are saying "something is wrong and I don't like it". You are not investigating the problem, identifying whether it is Predbat causing this or whether it is the inverter behaviour causing this because of some mis-configuration.

I suspect there is an mis-configuration somewhere in the inverter config (possibly in the predbat instructions to Solis), but at the moment I have no idea how to resolve this.

I'd suggest first of all you need to zoom in the graph to say a 10 minute period. Look at the Predbat logfile and identify what Predbat says it is doing with the inverter and look at the HA inverter controls, see if you can correlate what Predbat says it is doing with the behaviour you see on battery power graph. Look at the Predbat status, what is it set to over that time period?

Predbat sends commands to the inverter every 5 minute run so that would be somewhere to start, see if the inverter is doing something more frequent than that, it's definitely not Predbat.

When you do come back with more detailed analysis please include your apps.yaml file so we can see the config setup more easily than the debug file.

Couple of other things I notice from your logfile:

• it looks like you have days_previous set to just 14, so predbat is taking your load from a single day 2 weeks ago? Usually better to have multiple days to average over
• please turn debug mode off, it is writing voluminous log files and you can't see much happening due to this
• what I do see in the logfile fragment is Predbat in the 2 runs that are included leaves the inverter in Demand mode. It's not swapping mode to charging or discharging. Soc target is recognised as being 10% on each run