The game is still in development. There will probably be lots of time-consuming tasks later that make things difficult. They can always re-balance food and water later if they feel the need to.
I would agree that if they don't do the "physical-addons" I mentioned, then they should at least give us more module slots. But I still think that pressure integrity should not be a slot upgrade but a upgrade to the seamoth itself.
A reason to have a battery early on would be to store up a decent amount of energy from solar panels during the day for your base at night. There should be more things that continuously drain power. The water filter does this and when bases have l…