I'm using ElementalXs lollipop build on cyganomod, not timurs for the sweep2wake&sleep features if behavior is not AC current based. Experienced a similar pain with power fluctuations so I set out to find the best way to 'clean' up the power. I wasn't flattered with the idea of putting that much constant draw on the battery via a fused splice, so have been exploring mobile chargers that support pass-through charging. The first small el cheapo I tried would not switch fast enough at times, such as when the battery pack or tablet would reach full charge. Information regarding pass through support and ratings is cagey outside of some high dollar items.
Currently I'm testing a lime fuel LP150X that has worked flawlessly for about a week so far. Btssm has not had any communication issues since 'conditioning' the Usb power. Even though it will only charge at 1a when using pass through it has kept itself and the Nexus charged comfortably with 'deep sleep' profiles thus far (incl. sub 10F overnight temps!). I'm hoping to take a road trip this weekend and be able to see if it will be a strong enough battery pack or not when the tablet is really working hard. The Zendure A4 was the other promising candidate I had in mind.