Applies to the 580EX II.
The 580EX was recommended to use a dummy battery in the gun to get the full benefit from the pack ~ was never an aficionado of that myself. The flash flattened its own batteries first but boosted by the pack.
The way I use mine, it's still moreorless the same way and I've found when I run out of juice, simply swap out the batteries from the pack to the gun an away you go again. I rarely carry any spares!
I've let it setup whatever way it came, happy out, so have not looked in detail, but the whilst I found the manual incorrect in practice for the 580EX it is configurable and works as stated in the manual for the 580EX II.
Actually, I have a 580 EX II so it is recommended that I can leave regular batteries in the flash unit while the CP-E4 is attached? can you use rechargeable batteries on CP-E4 and regular Alkalines in the 580 EX II or do all batteries have to be the same type (rechargables or alkalines)?