I know this has been sugested in earlier threads, however, as i read those, i find it too difficult for NF to reprogram submarine concept of Air to Batteries. Me, I suggest a simplier one, and that is to give submarines a limitted movement or number of "steps" while dived. This concept is also the same with the other battery suggestion but they suggested complicated measurements of how batteries deplete. For me, change submarine air to limitted battery steps, much like the air, except that it only decrease while cruising underwater. That simple. I think it just needs a few reprogram of NF and change air  gauge to battery gauge/meter (just a graphic mod by NF). Higher level submarines of course, has a lot of underwater "steps" compared to lower level subs. What if the player is too coward to surface and will just stop underwater useless because his sub has low battery? well he can be detectec by auxiliary ships be HHed,  im sure he doesnt like that. What if at the end game he is the only one left? well just leave him there and retreat, the winning team still wins as wins are based on team attack, not on last man standing. What about critical dive? I suggest, leave it as is(he can critical dive again and again even he is not moving and would not want his battery depleted) or if nf can do it, make critical dives limitted depending on submarine tier (E.g higher level tier can do more crit dives than lower levels) or make crit dives equally limitted, like 10 crit dives per sub is only allowed, after that 10, lets assume comp.air is depleted and crit dive is no longer available and he has to resurface  for a duration of time to get 10 crit dives again. Of course, batteries are rechargble based  on planesmen and while surfaced. So? its just simple but i explained it thoroughly.thanks