Will I have enough thrust?
QI’m looking to replace my two 85 amp hour bow thruster batteries, but my local chandlery only does a 75 amp hour one. Assuming they physically fit, would there be any problems by going from 85 to 75?
The loss of 20Ah of capacity is not the problem it might seem because bow thruster run time should be strictly limited to ensure it does not overheat.
For a given run time, you would be discharging the new set more deeply than the old set so, in theory, it will use up their cyclic life more quickly. However, sulphation usually kills batteries before running out of cyclic life.
If they are physically smaller, you might have to pack the new set with pieces of wood to restrict their movement.