[HELP] Modding S class battery recharge

[Warden]

Hi, after being incredibly annoyed with the speed of the S class battery recharge I tried quadrupling the diesel HP of the sub using MiniTweaker. This more or less fixed the problem of the battery recharge taking FOREVER (it's still slow, but bearably slow now), but it apparently had the side effect of making my sub significantly slower when operating on the surface. For instance, if I set speed to 8 knots the sub will do 5 knots and so on. (I should point out that this behavior is constant regardless of whether or not I'm charging batteries.)
Does anyone know of a way to reduce the recharge time without this annoying side effect? And also, does anyone know why this is happening?