How long do you leave Smurf on a mooring for ?.
If its a few days, or even a few weeks in summer forget the pump just leave the bung in and bail out when you get to the RIB.
I left the pumps off Tigger II for over a week (by mistake) this winter and we got very heavy rain many night but their was only 4" of water in the RIB when we got back.
Also if filling the RIB with water has got to the battery and you cant seal it I would recomend replacing it with a sealed gel cell.
Sooner or later (sooner if our record has anything to go by) you will stuff your RIB into a wave, which will fill the RIB wit SALT WATER
and this really kills batterys if it can get access.
Most sealed lead acid will survive a long dunk with no problems.
You need to make sure it will supply the cold cranking amps but I think this is a range called REDTOP, REDSTART or somthing like it that are sealed and designed for starting.