Well... I didn't get much better runtimes from a fully charged battery. After about 15 minutes the monitor (Lilliput LCD) started getting scan lines and then shut itself off.
I ended up with one of these guys from Cabela's.. It's fairly heavy so it might not be an option for some rigs, but in my case it neatly replaced the counterweights on the back of the bottom sled.
I've run the monitor for hours and no sign of diminishing. One drawback with the included charger though: it's a slow charger so it takes 12-15 hours to charge, and it can't be left on indefinitely. Over 24 hours will damage the battery according to the "manual".
My spine will definitely give out long before this sucker.
I think I may have screwed my battery up the other day. Everything had been working fine, but I put the battery on charge and went upstairs. Came back down about 20 minutes later and smelled something burning. I bought the Liliput monitor and the silver battery mentioned in this thread about a year ago. Both came with a cord that are exactly alike and will fit into either device, but each have a different amp rating. Normally the monitor lasts as long as I'm filming, but today it cut out completely after about 20 minutes and I had to use the fold out lcd on the camera. Will try again later after a full charge to see if it's busted. My advice is to make sure you label your wires so you don't destroy your equipment, or worse, cause a fire.