Predbat always charges to 100%

[AberDino]

I've got a (gen1) GivEnergy Gateway, 2x GivEnergy AIOs and a third party solar PV inverter. Predbat is set to "Control charge & discharge" with switch.predbat_set_export_freeze and switch.predbat_set_export_freeze_only enabled, because my export contract does not allow brown energy. I'm on a ToU import tariff which enables cheap charging overnight.

Even though I've got ample battery capacity, Predbat always charges the battery to 100% overnight. Looking at tomorrow's plan, the prediction is that my battery will be down to 69% at the end of the day, before it gets charged to 100% again (I use a 48-hour plan).

I don't think there is anything wrong, I'm just keen to understand Predbat's logic for always charging to 100%. Perhaps it is because it knows that there is no headroom required to store solar energy, and to cover all eventualities and be on the safe side, the battery might as well be charged to 100%? I enabled debug logging to see if there was anything obvious in the log, but I'm afraid it contains too many details for me to work it out. Does anybody else have any experience with this and what to look for in the debug log?

Ideally, I'd like to run my AIOs down to as-close-to 4% as possible every so often. Any suggestions on how I can achieve that without exporting (too much) brown energy and/or having to use electricity at peak times? For example, I could put Predbat into monitor or read-only mode, set a manual charge overnight to a level which should mean the AIOs get drawn down to 4% the next day, and then properly enable Predbat again after that.