the stick pack is nimh, , so can be fast charged if required at a rate of several amps, - the capacity of the battery you have is 3.3 amp hours,( so for example if you motor was to run on load and draw 3.3 amps your nihm battery would be able to supply power for one hour) -
its a 6 volt stick so in theory could be used to power your boat... it will be alot lighter i guess than your lead acid battery... this may affect the trim on your boat so do some testing first
the lead acid cell cant be charged quickly, it needs a trickle charge of about half an amp per hour or there abouts, -
you dont say what cpacity the lead acid battery is ... but i guess it may be higher than your stick pack so again in theory it will power your model for longer than the stick pack....-( using the same example if you lead acid battery was 6ah or 6 amp hour capacity you would get nearer 2 hours run time, so nearly double that of the nimh stick pack )
there is no reason why you couldnt swap them over, just be careful with trim and ballasting- you may also need to modify the plugs that come with the speed controller to accept a stick pack