I suspect the figures that you are quoting are not accurate. If our battery had run out of steam after only 6 hours, I'd either have bought a regulator for the motor or a bigger battery.
Without hunting for my manuals, I have had a quick search on the net for power consumptions of my electronics.
VHF quoted as 0.5A, GPS 0.8A at max power.
Presuming 1.3A and the 25 AH figure you quoted, this should give give me at least 19 hours operation for those two.
The sounder uses 0.8A at max power, very unlikely in a shallow North Sea, and is switched off except when motoring.
I suspect the pump uses a fraction of what you think. When testing the efficiency of the PWM, I had it pumping water for over 24 hours on a 7Ah alarm battery before I got tired of hearing running water outside and switched it off.
Having checked, the battery we are now using is a Leisure 685L. It seems that this is not 50AH but 85 and costs / weighs in at about the same as a 50. That said, we had quite happily been using Halfords 50A batteries in our boats up until we replaced them at the start of the summer. The old ones lasted for over 3 seasons before noticeably tailing off.