As you can appreciate, the huffy hullis not too big, so space and "weight" [more importantly] is at a premium.
It ia difficult to advise on battery size/capacity as its all dependent on the motor size and battery drain due to its length of time used on the water.
Its a difficult one to try and balance out. weight versus sailing time
if you put too much weight in, the hull will sit too low in the water and the semi surface piercing prop wont be able to do its stuff, plus if you try and balance the weight forward towards the nose, you can make the boat prone to diving like a sub given half a chance!
It may be better to keep it light and have to reluctantly swap batteries more often, but at least the boat will skip across the water like a scalded cat [ha ha].
if you go for bigger/heavier abttery to increase sailing time,, as said above, the slightest wave or even crossing over your own bow wash can put the nose in to the water and its "dive dive dive !"
But, release the throttle and within seconds its bobbing back up to the surface "right side up" again and ready for action, no harm done.