I was looking at the mark ii, 5d vs 1ds, I went for the 1ds and the build quality is amazing and really just feels right in the hand, the 5d even with a grip just doesn't feel the same imho, I've never found battery to be an issue it last for ages, I've found my self shooting days and not charging in between.
Now don't get me wrong, it's an old camera, the LCD sucks and you can't depend own it for reference or image quality, but once you have the confidence in the camera it really just to check level and exposure burnout but you get used to it, also the two button approach to everything is very alien at the start but you get used to it, and know when i pick up my 40d I'm pressing two buttons without realising and then getting confused why it doesn't work lol.
it gives an amazing look to all the photos you take, it's hard to explain, somewhat less digital and more traditional look to the shoots, even at high iso it almost looks like film grain apposed to noise, I'd give a 1ds ii a big thumbs up, I love it