We try the Sunpak TR-2000 flash power pack
Connecting battery to flash: High voltage connections, such as this one on Sunpak's 5000 AF flash, are easier ("plug and pop") and more durable than the less-convenient, jerry-rigged low-voltage adapters that slide into the flash's battery compartment (not shown.)
What's the TR-2000 like in the field? Our first charging took about six hours, and we monitored its progress via the power cluster's five-LED power gauge and via the System Status LED on the pack's control panel. The status LED was unusually informative telling us: that the unit was ready (solid green), charging was complete (flashing green), charging was underway (solid red), charging was required (red/green flashing), inadequate voltage for charging (solid orange), the unit was in its sleep mode (no LED), and, one we never encountered, an error had occurred (flashing red).
The TR-2000's 24-ounce weight is easily managed (see photo caption for complete dimensions). Thanks to its curved edges, it's one of the most comfortable power packs we've carried on our belt. (The TR-2000 comes with a belt clip and shoulder strap.) If you must bend at the waist, for example, there are no sharp corners to jab into your side or abdomen. Its inside wall is curved, so it hugs the contour of your waist, where it's less likely to catch on chairs (or people!) as you navigate a crowded room. It also creates a less-noticeable bulge under a tux jacket.
In operation, the TR-2000 worked flawlessly for us, providing instant flash charging with consistency and reliability across hundreds of flash exposures per charge. We never missed a shot. Using Sunpak's 5000 AF flash, it was a simple matter of plugging the power cord from the TR-2000 into the flash unit and firing away.
Should you consider the TR-2000? If you already have trouble juggling a flash and an SLR, you probably don't need another box, cord, and shoulder strap (or belt clip). Stick with AAs. If you're a coordinated photographer who can deal with a little extra gear, however, you can reap major benefits from the TR-2000, especially if you're missing shots due to sluggish flash charging. Selling for about $300, the TR-2000 may ween you from AAs forever.
See Portable Flash: "What to look for in a portable flash unit."