I have often wondered: Do expensive batteries have more juice? So I bought the three brands available at my local drug store, and decided to test them. These are three new 9-V batteries, driving a resistive load of 3980 Ohms, and monitored by a data logger. The test is still running, so I will see how long it takes to really kill them. Meanwhile, here is the graph. "Walgreens" is the store brand at the drug store. I have always replaced preamp batteries when they got down to around 8.5 V. With one more fresh battery (this testing could get expensive), I will measure lifetime in an actual preamp.