[CentOS] way to replace DELL PERC 6/E card???

we have several R900 servers with PERC 6/E card in it.  Recently it we getting some message on /var/log/message say change to "write back" and change back to "write through".   

We figure out it is PERC 6/E card battery weak.  My questions are:

1. some battery only use one year (some even shorter) and already this problem.

2. How come PERC 5/E does not have this issue?

3. where is DISK array information store for PERC 6/E?  I did NOT see NVRAM on PERC 6/E card.

4. when replace PERC 6/E card and power on server sometime it will ask you "import configuration" ans some time it won't.  Why?

5. When replace PERC 6/E card and power on.  Server ask "import configuration" should I answer "yes"?

6. where can I find documentation which mention "import configuration"?

Thanks.