Have you tried charging them (plugging in or driving)? Lithium batteries typically have a BMS (battery management system) that automatically disconnects the battery to prevent damage to it due to overdischarge. Applying a charge voltage to the battery should re-activate it.
Some Lithium batteries shut down at low voltage and need a certain type of charger to "wake" them back up. Do you think this is what has happened to your battery?
What brand battery do you have? Can you contact them tomorrow?
If your PW has a GU, maybe just driving around with your Li-Ion batteries turned on will charge them or wake them up? Worth a try if you haven't done so already.