In preparing my 12" PowerBook G4 (2003 model, 867 MHz, bought in June of 2003,) I decided to test its batteries. I have two, the original battery, and a second I picked up a few months later when I realized I needed more than one battery's worth of life per day (at the time my job was on-site computer repair, and while I had the ability to plug my laptop in in my car, I often didn't have enough time to recharge enough to go the full day.) For comparison, I replaced the PowerBook as my primary machine with a MacBook Pro, ordered in January 2006, within in an hour of the Apple online Store coming online and making available orders for the very first Intel-based Macs. That MacBook Pro (2 GHz Core Duo, 2 GB RAM,) is still my wife's primary machine. (I stopped using it when I got a "conventional office job" in 2010, followed by getting an iPad, which has served just fine as my primary mobile computing device.) However, that MacBook Pro is on its seven battery. The first six were all replaced by Apple under warranty. (Note, like with the PowerBook, I bought a second battery for it, so it has been a game of 'leapfrog' replacing each battery, then the second, then the first's replacement, then the second's replacement, etc, etc.) Each of those six replaced batteries had degraded to the point of holding less than 50% of original charge before reaching 100 charge/discharge cycles. (Apple's 'line' was that it should hold 80% at 100 cycles.) Apple was great, doing the last warranty replacement in 2010, well after the warranty was expired. And thankfully, battery #7 has been a good one. It is now on ~250 cycles, and still holds about 80% of its original charge. But, back to the PowerBook. I decided to test its two batteries. The first one I tested happened to be the 'second' battery I bought. It has 320 cycles, and has a maximum capacity of about 2700 mAh (about 50%.) Then I tested the original battery. It is at a whopping 479 cycles, and claims a full charge capacity of 5907 mAh. Which is truly insane, because from what I can find, the original maximum capacity should be either 5200 mAh or 4400 mAh. (Sources differ.) I'm in the process of testing it now by running it down to see how long it lasts. Which, if its current estimate holds, it will still be running when I wake up in the morning... (I test in a "low drain" setup - brightness at 1/4, all wireless off, but all sleep modes off.) But, I'm at over an hour in, and the drain rate is steady. It seriously looks like I'll get over 7 hours of life. (Of course, the other possibility is that the estimate on how much capacity it has is off by a fixed amount like 1000 mAh, and it will just unceremoniously die when it reaches that point, with no prior warning.) Edit: Well, it has now been two and a half hours, and the time estimates, drain rate, and charge remaining is in line. Claims to be over 5 hours of life left! Obviously, this is a "absolute minimum use" situation, but if you are, for example, a writer, this should be a feasible use case. Edit 2: It made it about another hour. I had just finished my "every 10 minutes" recording of battery status. It had dropped to 3301 mAh remaining, then about a minute later, it went to sleep. I plugged it in, woke it up, and it says 0 mAh remaining. So now I've unplugged it again (it went immediately to sleep,) and am going to let it sit in sleep mode until it fully dies. Still, 3 hours 20 minutes is nothing to sneeze at in a 10.5 year old battery!