ILife A4 4 beeps error

Hi!

I have an A4s that stops after 2 mins of running, spins the brush and gives 4 beeps.

I've cleaned the brush gearbox, put a new brush, even replaced the brush motor. The unit still has the same error after repair, but the brushes are spinning freely even when the robot is giving the 4 beeps.

Looks to me like a logic error (mainboard) or battery issue perhaps (battery declared at 14.8V, but measures 16.7V on a full charge)?

any ideas/suggestions?

Thanks!