This skill is remarkable for how poorly the tooltip explains what happens (and why). It is also remarkable for how little return on investment you receive (judging by discussion of this skill in other threads in this forum). So if I were a Cryptic Dev reworking this skill, here's how I'd restructure it.
Global Cooldown to Auxiliary Systems: 20 seconds upon activation of skill to charge Skill Battery or use of a Devices Battery
Global Cooldown to Devices Batteries: 20 seconds upon activation of Battery charged by skill
Skill Cooldown to Auxiliary to Battery skill used: 150 seconds - 10 seconds per BOff skill point (so 140s @ 1, to 60s @ 9)
While charging Skill Battery, Auxiliary Power level is reduced to zero (it's all being diverted into the Skill Battery).
Skill Battery "size" when charged is a fixed value no matter what Auxiliary Power slider was set to before use of skill.
Auxiliary to Battery I creates a "smaller" Skill Battery than Auxiliary to Battery II ... but Auxiliary to Battery II "charges" its Skill Battery "more efficiently" ... meaning that charging duration (during which Auxiliary Power is drained to zero to charge Skill Battery) is effectively the same for both skills at identical Auxiliary Power settings. This also means that each skill "produces" only a single "size" Skill Battery (each) which in turn only need a single tray slot (which are already being overwhelmed with other options needing hotkeys!).
Time to charge the Skill Battery is determined by the Auxiliary Power setting level while charging the Skill Battery. A low Auxiliary Power setting makes the charging process/delay take longer ... while a high power setting makes the process/delay complete more quickly.
Skill Battery, once charged, remains available for use for 6 seconds + 1 seconds per BOff skill point in Auxiliary to Battery (so 7s @ 1 to 15s @ 9).
Auxiliary to Battery I produces a Skill Battery that, when used, has a duration of 5 seconds + 0.5 seconds per BOff skill point (so 5.5s @ 1 to 10s @ 9)
Auxiliary to Battery II produces a Skill Battery that, when used, has a duration of 6 seconds + 1 second per BOff skill point (so 7s @ 1 to 15s @ 9).
Skill Battery Power Boost level to weapons, shields, engines and auxiliary power is enhanced by Engineering Team Leader, Starship Auxiliary Maintenance and Starship Auxiliary Efficiency captain skills.
Hmm auxilary does improve the battery itself. If you max all aux system skills. The aux to battery skill, with max aux creates a battery for 188s, wich last 10s and gives +85 power.
My only grip with that skill, is that the created battery shares cooldown with normal batteries, and the cooldowns are a bit borked also. The duration of created batteries should be twice as longer, and it shouldnt share cooldown with item batteries.
Oh and also, using engineering team before using the battery, improves it.