After starting with the 400s myself, I think it's a mistake to do so. Can you get most of a day out of one? Yes, but.. The voltage they produce drops off relatively rapidly during that time. They work very well when freshly charged, but not so well as they discharge. There were several occasions when I thought there was something wrong with one of my tanks when the problem was in fact the battery being low, and it never got to the point indicating it needed to be charged by blinking.I started with their starter Triton kit with 2-400 batteries but in a matter of days I knew I needed to step it up to be 100% happy. Not that the batteries were bad or didn't last as they did for almost the full day on just 1, but I know myself and I would of upgraded later anyways.
That said, I'm keeping mine despite having ordered some Triton spinners. The 400s do recharge very quickly, and they are such a handy size that they're ideal for "stealth" purposes. A Triton tank on a 400 literally disappears in my shirt pocket (it doesn't stick out at all), and it can be "palmed" as well.