I will add my experience,
Over three years with two NP-E3 batteries, I have noted a drop in the number of pictures I can take before recharge, but it is still around 1500-2000+ per charge so no worries yet (It was between 2500 and 3000 ). One of the two seems to run out a touch faster, but I can never keep track of which is which. I got the second battery less then a week after I got the camera.
In my case, i shoot until I get to the blinky light, switch out the batteries and immeadiately recharge the used one. As soon as it is charged I put it into a pouch I have with the cap on it. If traveling and don't have the recharger, I leave the cap off, so I know it is discharged and that one gets charged first when I get home. So far, I have never drained both batteries to blinky status at the same time, but I did get the second to low power once.
And scary was the first time I wasn't paying attention and ran the battery out. Nothing more fun then hearing the mirror go up and then no-recocking. Heart stopped until I swapped batteries and the camera reset as it should. I am sure I am not the only one and I haven't done it since.
So 3-years, still hold at least most of the original charge, no problems.
Just my experience,