Well, what's the point in the game having slowly recharging batteries if you can just skip the wait? Why not let them recharge instantly in the first place? Note that sleep is not necessary in the game (you never get tired). I guess it could make some sense if crafting a bed was difficult somehow, but I don't remember that being the case.
I use to make two sets of batteries, exactly so that I don't have to wait. When out swimming around I use one set, while the other is recharging back at the base. Growing food might be an even better example, because you may risk starving while the plant is still growing, forcing you to plan ahead.
Both games are worth full price. Also check that you don't have ARK already, I got mine free on Epic.
The differences between them are:
In ARK animals are your biggest threat, in Subnautica it's drowning and dehydration.
ARK seems much bigger, both in playing time, area size and number of animals. Subnautica's gameworld instead has much more vertical (deep sea) topography, so the total "volume size" may even out between the two games.
ARK has more realistic graphics, while Subnautica's colors seem a bit childish at times (but you get used to that, and it still looks very nice).