Even before I got my 1D Mark II, I spent some tim browsing the internet and looking for related information. It was good decision, because I found one important aspect of the battery that I didn't know before. As every car has it break-in period, it seems NiMH batteries have similar period or rather specific techniques how to get the most of the battery pack. There is an article and forum thread that describe this aspect and steps that you have to do when get a new NiMH battery:

• D1X Tip: breaking in the EN-4 battery
• 1D Mark II - Initial battery conditioning?

Using those tips my 1D Mark II can get over 1200 shots from a single charge of the battery. Isn't it great? :)