@Mat - do not worry, you are not going mad. I have an GivEnergy AIO and I suffer the same issue. I can set the Hold Charge button to On and choose any value 0 or greater than 0 and my setup just ignores it too.
The only way I have found to successfully get a true battery 'Hold' to function as expected - i.e. to stop draining my battery, is to manually turn off Eco Mode at which point the desired hold state is reached - we then pull 100% from the grid until I turn it back on again.
@admin I believe I have mentioned this to you previously but got lost in other topics that were more a priority at the time.
For me, for a GivEnergy setup like mine, I would like an option in the charge settings window, a toggle that says, Eco - Enabled / Disabled so that I can ask WW to set the Eco mode to OFF for the duration of my window and then charge for the selected slots, then re-enable Eco to On when the window ends.
Do you concur both of you?