The toilet will continue to flush if you have a power cut. The old-style PCBs will allow the toilet to continue to flush until the batteries are drained to the extent that the toilet will not flush anymore.
The new PCB (from April 2019) will protect the batteries by stopping flushing after 25 flushes.
It is important that the batteries are not allowed to go flat. If they go flat, they must be recharged within 24 hours.
In the case of a power cut, it is also possible to empty the pan by pouring a bucket of water into the pan.