Following up on this post, more from mrailing:
The readout on the battery life remaining is an estimate of the actual reading. You will notice this after a long call it might jump way down and then 20 minutes later it will come back up 10-20%. The CPU is estimating the life left with the current load on the system.
The best thing to do is get a feel for the system, fully charging every night for a week and see about how many hours you get on a charge, use this as your baseline, especially over the first couple of weeks owning the device (since you will be playing with it more than during this time than you will weeks later when it’s all setup the way you like). For me, I can easily go from morning to night on a charge, with the occasional topoff in the car or at my desk. I got in the habit of doing this with my i730, any time I am around a charger, plug it in. Li-Ion batteries are not affected by any memory issues, and it’s actually ok to top them off. A quick 20-30 minute charge can bump the life substantially since Li-Ion batteries, depending on their size, typically charge to 80% in the first 30-60 minutes, and then trickle charge to 100% (which is why many of you are seeing 80%…). It takes almost as much power to charge a li-ion battery to 80% from 20% as it does to 100% from 80%. But when you use your battery it drains slower in the first 20-40% then it does in the last 60%. This is just how li-ion batteries drain and work. They provide equal power over a greater period of time compared to Ni-MH batteries, but work a little different.
So, use it, top it off, don’t run it flat, and you will have good battery life. If you search the i730 forum for “battery life” and use my username in the username box, you can find lots of explanations of best usage of a li-ion battery and a little more detailed explanation…