Test-driving these ships, the power states that it drains 75 weapon power upon completion.
However, both ships were using the attack preset, and were usually around 100 weapon power when firing weapons, with 85-ish being the lowest observed. The power drain from using the Lotus would be steep, but it shouldn't drain all power.
But instead, it drains ALL weapon power, whether you're at 80 or 125. And it keeps your weapons offline by staying at 0 for a few seconds.
Further testing has shown this is a consistent side-effect.