I have had a G700 since they came out, I find the battery will last me 4-5 days of normal use, which is I reckon 5-6 hours. When I have been home all day and spent more or less the whole day on my computer obviously I have to charge it more often. I only find the battery life starts to become an issue when the Ni-MH batteries have gone through too many charge cycles, I wouldn't recommend you keep charging it when it doesn't need it, for this reason.
I have just ordered a pack of 4 Eneloops. The life of the Duracel 2650mAh rechargeable I have had in it around a year now, is a bit silly, it was great at first but now it goes into the red after about four hours and will run flat in around twelve. However, it gives you dire warnings of battery doom long before it actually runs out.
I use 1200dpi with 333mhz polling rate for desktop use. I switch to 1800dpi and 1000mhz for gaming ...or my Death Adder.
Really I think the G700 is a great all round mouse, but it's not a 'great' gaming mouse, The Death Adder is more responsive, lighter and a better shape. The shape is what makes me keep considering a Mamba, as I bought a Death Adder in 2006 when they launched a bought a DA 3.5G to replace that a year or so ago ...it is the best shaped mouse for me I have ever used, bar none. The G700 is 'similarish' but not the same, although far, far better than the G500/510/518 shape that so many people love, that shape causes me discomfort after a fairly short period.
The G700 is my jack of all trades mouse, it works on my armchair, travels with me and works on my desk, the Death Adder is used only on my main desktop pc for gaming really.
On a related but slightly different note, I ...for what reason I don't know, bought a Corsair M30 a few weeks ago to see what they are like, I thought the shape looked nice and they have a very good sensor ...what a bag of **** that is, the sensor is good but the build quality makes Razer's very worst efforts look amazingly good ...and we all remember how well made the Diamondback was eh, you could do worse for 30 quid though.