I created a set of nano armor a week ago, that was at level 1, now I am level 33, seen a lot of combat, had creepers explode in my face, ghasts and blazes setting me on fire, zombies eating my face, spiders trying to envenomate me, etc and I've not had to recharge, after the initial charge, the nano armor. The armor bar is still full and the green bar on the armor pieces is still full. This is weird, it's cool for me, less I have to worry about, but still kinda feels like cheating. 
[IC2 1.71] Nano Armor not taking damage
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Now that you mentioned it, I also noticed this, I just thought it took damage really slow, but then I got quantumsuit armor and it degraded pretty quick.
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i also agree i had died many times then i made the armor and the only time i ned to recharge is when im an idiot and jump down my buildcraft quarry hole or some thing then i retrieve it charge it and im good on charge until i die again. please fix this bug its almost as much of a cheat as tmi.
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Yeah I'm having same problem too. I'm using the Technic pack and when I had it automatically update to the latest version of IndustrialCraft I noticed I was invincible with the nano armor. Like you said it is pretty fun at first but after a while it takes all the fun away from the game. I have since downgraded industrialCraft so I can die again.
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I can also confirm this bug. I crafted mine when i was level 30 ish and now im level 80 and i have yet needed to charge it other than the initial charge. I have heavy combat in that time frame also.