Coconut battery was recently updated to 2.6 to work in Leopard. See what your new info is with it.
That said though, when I was using 2.5.1 with Leopard, I found that the mAh were pretty correct, it was jut the age of my mac and load cycles that were wrong.
You can also get Battery Health Monitor or just look in System Profiler under Power for the information.