Leisure battery questions

Leisure battery question (pollensa)
My Leisure battery has gone bad and would not hold a charge so have removed it until a new on arrives, however when I flick the master switch on the zig unit it is showing 12v+ (my starter battery I presume) is this correct or do I have a problem with ghe splir charge systen(can see the live that comes from starter to Leisure)
Update/further issues

Just an update, when cleaning inside today I flicked the switch on fridge and it started( not on hook up, no leisure battery connected, engien was off) so was running off starter battery???

When I connected new battery got a  big flash/spark, how have no 12v at zig. Checked two fuses next to battery 30amp blown replaced it but still no 12v.

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Have you checked the (2?) relays in the block by the LB under the driver's seat?

How would I go about testing these?