There's nothing worse than running out of batteries half way through a long troop and your helmet lenses start to fog up. Because of this, I elected to use a USB power bank. I followed ukswrath's Gen 4 tutorial over at FISD to create my setup. It's nice having 12v and 5v power that will last all day and then some. My power supply is an older model though so I've looking at cheaper/higher capacity MaH replacements on amazon. Right now I have my eye on this:
https://www.amazon.com/dp/B01MXQCZAP/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=2U47PYX41741F&coliid=I889MM0YOCJWY
What are you guys using?