The flash uses four "AA" batteries, which go into a plastic holder that slips into the battery compartment. Vivitar sells extra holders and I find it very convenient to have the batteries already arranged in the holder when having to change quickly in the middle of a shoot. With alkaline batteries you can expect around 100 to 150 full-power pops (my test with new batteries gave 128 full-power firings), though refresh times will go from under 10 seconds with new batteries to almost 20 near the end. Using 2500 mAh NiMh rechargeable batteries, I got 212 full-power pops, with faster recycle times as well (about seven seconds to start, lagging to 12 near the end of their charge). With close subjects in auto mode, or on 1/16 manual power, recycle times were as short as one second. The flash has a guide number of 140 (ISO 100, "tele" 105mm zoom position -- i.e. with the head/sleeve pulled all the way out -- in feet), which puts it at the low end of similar-sized units like the Sigma EF-500DG Super (GN 165), Canon 580EX (GN 191), and Nikon SB800 (GN 184). The Vivitar is, however, by far the lowest-priced unit of that bunch, with a street price of $89 (the Sigma is $199, the Canon is $399 and the Nikon is $325).