Power supply advice

[munge]

So... I have a 2018 F15 in the UK and have extra lighting (emergency flashing lights) installed which currently come off the main battery in the back to a circuit board that distributes power, controlled by a switch panel at the front. This switch turns itself off when it hasn't been used for an hour, but frequently causes the "Battery Discharging" warning to appear on iDrive.

It doesn't seem to affect any functioning and I can dismiss the warning with the iDrive button, but it's very annoying.

Any suggestions how I can get round this? I'm thinking either coding to out? Or maybe having an alternative power supply in the car for these lights?

Current draw is at most around 5-10A (not sure exactly) so not massive.

Am sure somebody somewhere has something powered up via the battery and has found a way round this.

Any ideas gratefully received.