Some info asf:-
6V 4AH
Place of Origin:China (Mainland)
Maintenance Type:General
Voltage:6V
Size:70mm *47mm *100m
Nominal Capacity:4Ah
Sealed Type:Sealed
Weight:0.67kg
Usage:as long as 6V4AH
Cycle use:7.25-7.45V(25℃)
Standby use:6.8-6.9V(25℃)
But i think you minimum need 12V 7A, if you use 12V motor,
NIMH more better wow.. only my suggestion only.
you use 6V.. and output sure not 6V and will slow down proportional if you use lead-acid battery, but NIMH can output exactly 7.2V all time if you have a good charger
Some more experience comments is you can use a parallel card to connect 2 5000maH NIMH battery (7.2V), it can play for long time and enough loading in the tug boat... but need more experience to use parallel card....