I personally would rather be able to monitor the levels. Usually I just run one set of batteries on the 1st set and another on the 2nd set. For festival season, I just bought a 5V Lithium Ion battery pack that puts out 44WattHours. That should be able to allow me run all day.
$99 Key Features:
High capacity. Most Digital Cameras/Video Camcorder's standard batteries only have 5Wh~10Wh capacity. This battery has
44Wh (Watt-Hour) capacity. For reference, an AA battery has about 2.7Wh capacity (1.8Ah at 1.5V). This may help calculating your expected run time.
Ultra light weight design.
Compatible with
Devices which require 5V, 8.4V or 11V power supply, such as network routers, BiX Pocketsize USB or Firewire hard drives, BiX Slim USB or Firewire Optical Drives.
Compatible with following Cameras/video cameras: Sony, JVC, Panasonic, Fuji, Olympus, Nikon, Casio, Kodak, HP, Minolta.....
as well as most cameras or devices which require 5 to 12 volt power supply.
No memory effect. Can be recharged at any time regardless of the amount of discharge.
Built-in batery gauge which displays power level of the battery pack.
AC quick charger included. Temperature and over-voltage/current protection.
Universal camera cable included. Compatible with most all digital cameras/video cameras or equipment.
Can also be used as an external power supply for any device such as portable Radio, CD/VCD/ DVD player etc...which requires 5 to 12 volt power input