I think that the battle interface should have your amount of crystals on it, so that you know what you need and how many crystals you got when you collect crystal boxes and gold boxes. Tankers had this before, in the Flash Version, but in the HTML5 Version there is no way to check how many crystals you have.

A new battle mode called Duos would put each tanker with a partner and they would work together. There would be a max of 10 Duos, (for 20 tanks). *Also* The Duo Teams would not be able to kill each other, so basically a Mini-Team. The kills would add up and points would add up, and that's how they would rank on the list at the end of the battle and when you press 'Tab'. *IMPORTANT* Even though they are added together, they would still get their individual crystals. This is so that if you get paired up with a tanker who doesn't fight very well (No offense to them), they can still get their equal amount separate from their total Duos Score.