elinchrom ranger pack system?

I am in interested in purchasing an elinchrom ranger pack system. I'm

wondering about battery life (overall longevity as well as shots between

having to recharge). In general, I am looking for any hands on experience

people have with this system. From what I understand is that they make an

1100w/s pack and they have a small 2400 w/s head. Why is the head

capable of more power than the pack if it was specifically designed for the

ranger pack. Are older battery packs or heads compatable with the newer

ranger system. As you can see I have a serious lack of accurate information,

please help

Thanks