As of May 11th of 2016, the expected battery life of an anchor running the demo firmware powered by the batteries provided in the DWUSB kit is 6-8 hours.
As of May 11th of 2016, there is no way to extend the battery life with the DWUSB demo firmware beyond obtaining a power source with a larger capacity. If you do look for other batteries, please be warned that many USB battery power supplies will monitor the current drain, and for many of them, if the current drain stays below some arbitrary threshold for an extended period of time, the battery will stop supplying power to the connected device. As most of these USB batteries are made specifically to recharge phones and the DWUSB does not draw nearly as much power as a phone that is recharging its battery, most USB batteries will not work properly with the DWUSB.
If you do want to perform any long-term tests with the current DWUSB demo software, we would recommend getting some USB extenders and some USB to wall socket adapters. We will be looking into improving power efficiency for future demo releases, but for now, that might be the best alternative.
Oddly enough, it is actually receiving packets that takes the most power on the DWUSBs, not transmitting packets, so reducing the rate at which devices can transmit would not provide any significant gains in battery life.
As of May 11th of 2016, the current demo software does not support adjusting the sample rate.