I don't know if it's a Tekkit issue or MPS-specific or something with the energy conversion framework, but the energy tooltip on power armor items is off by a factor of 10. For example, I have a medium battery in my helmet set to the maximum storage of 100kJ, which is 100,000 (M)J or 1 million RF, which is exactly what I can put into it using the energetic infuser. The tooltip, though, says "10k", i.e. tenth of what it actually holds. Not a huge issue, but quite confusing (imagine my surprise when that helmet that I thought would be charged with 100k RF drained my fully-charged infuser dry in a matter of moments)
Also, the power suit items are able to draw energy from my flux-infused tools when their own batteries are empty. Haven't tested if it works the opposite way, too. I guess they share their energy pools, as the tools' energy is also factored into the number that's displayed in that little energy gauge on the right side of the screen. Bug or feature, I don't know, but it seems odd.