If you find yourself short on the batteries you need out in the field, you might want to consider this battery hack. With careful use of a pair of pliers or a knife, you can make 6 AAA batteries out of a 9-volt battery. If it's a used 9-volt, you might not get full voltage out of all of the batteries, but it could be enough to get you through a job. Also, if you have an older camera or light meter or even a pocket flashlight that takes the 394 (or LR45) button batteries, you might try this hack of a 12-volt battery to save yourself about $40. Keep in mind, though, that it's not a smart move to put homemade batteries in anything that's still under warranty, as anything DIY is sure to void it.