Just had this fault. Turned out to be the battery flat. The on board charger was draining battery and not charging when plugged in.
Charged truck from another charger. (not an on-board charger) connected battery to truck and working. Tested on board charger again and it was dragging the battery down. Even when plugged into mains and supposedly charging. Fitted new charger all good.

Q10 is the line contactor on the far-left top. Open circuit on the contactor. Replace the unit or repair associated wiring. The unit is the most common problem.

All depends which BT truck you have i suppoose :)

3:564 Low current
Allt stoppas direkt, parkeringsbroms aktiveras och huvudkontaktor öppnas.
The amperage is below the limit
value 100mA on the output to
brake (Q10)
* Low power consumption
or break
1) Check wiring and component after the break
Disconnect the battery
Visually check the wiring
harness
Using instruments, check
that there is no break in
any wire
Check the Ohms and the
Amperes of the component, compare them to the
setpoint values, and replace the unit if they are
outside the accepted
range.
Reconnect the battery.
Measure and check the
voltage for the activated
functions