I have been running 'whatevers' all brands...I bet I've gone through 80 of them in the past two years, maybe more, heres what I experienced...I run 40 disc, Iron off, Pro zero mode, anywhere from full sens to 3 clicks down, and I NEVER once have used the PP button, blue headphones...so I believe I am getting max hrs on account of my usage/settings...a guy can easily go through 2 or more sets of batteries in a week of peak season hunting...
I get @15hrs of total hunting time off a set...when they drop down the first bar, the second is not far behind, and any further down that that, the tones and strength of operation SEEMS to be compromised.

I've tried really hard to pay attention to this subject, and not just go on feelings.....One gold ring or chain can make or break a season, and I do not have confidence in the rig if it gets below half power for sure... ..
Theres a lot of life left in those batteries however, so I take them out and pop them right into my F70, which has a reputation of getting 40hrs per set, and it loves them, so I get another @15+hrs on them in my 70. The 70 runs them all the way down to zero without missing a penny...I do not want to miss the find of a lifetime on account I'm trying for battery life with the Pro, I hunt primarily GOLD jewelry with the Pro, and inland coins/jewelry with the 70...
Goldstrike just did a great post on the Minelab Quattro forum about Eneloop rechargeables...I'm gonna go that route...I have so many half deads that came out of the Pro, it will take my 70 a year or more to consume them all...so I'll run the rechargeables in the Pro until I use the half deads all up, and switch both rigs over to the Eneloops..
Mud.