Your compressed air will deplete submerged at 0 knots?

[XenonSurf]

I like SH5 more and more (with TWoS of course), the enemy escorts and incomming planes are the hell aggressive and do their job right, even with map contacts showing inclusive the arcs showing their sonar ranges, I'm not quite able to beat 3 escorts circling over me, quite realistic because I should have done my homework before
In one of Stoianm's tutorial videos, which I highly recommend watching, he shows how dangerous it can be to shoot at 90°: that's exactly where escorts will search you afterwards...

Then, with multiple damages I wished I had not installed these improved crew voices because the panic shoutings taken from 'Das Boot' didn't stop anymore. For more 'immersion' in the concrete sense, I whished the water levels would go higher than just 1/2 meter or so, with showing effects of the sub's vertical and lateral aspect angle, also effects by closing hatches and isolating compartments, but the game engine has to be limited at some point.

In such desperate situation I noticed that my compressed air was slowly going away while my sub was stabilized at Battle Station (F7) + silent running and 0 knots. Is it because my pumps or other devices were damaged or is it normal that CA is depleting when maintaining the depth of a WWII sub?

Also: Does anyone know what the F7 command (Battle Stations) really does compared to not activating it? In most tutorial videos Stoianm & co don't bother activating it.
Also what about 'Battle Stations level 2' ? Only thing I know is it's necessary to man and operate the deck/AA gun correctly, but else I hardly see any consequencial effects, does the crew act faster and more efficiently, e.g. during repairs and manoeuvres?

Thanks,