Hello and welcome to Club Motorhome. :welcome1: As to your query if I understand correctly the speakers use a 240-13v step down transformer therefore they will work on EHU via a mains outlet socket, but not from a 12v battery unless you use an invertor to provide the 240volt input so that it can be transformed down to 13volts.

Remember also that your 12v battery will only give DC (direct current) whereas the transformer will supply AC (alternating current) unless there is a rectifier incorporated into the tranformer unit on the output side between the secondary winding and the connecting plug
Best regards
Phil