uhm, personally I use HV capacitors on all pieces, with 200k energy on each.
I use heat plating and force generators maxed out on everything (force generators don't add weight).
I have pretty much everything else installed and I still move properly.
As a tip, in case it may help you, if you have an energy cell in your inventory the suit will drain power from it. that way you can remove the batteries from it altogheter.
Still, as long as you have solar panels, motion generators and heat generators in the suit you should be able to get more energy than you actually use.
I have yet to use the thunder gun as normally I prefer the railgun (it does enough damage for my taste).