You can replace with the power on if you are very careful.
If you want to do it with power off, make sure to do manual shutdown found in the Service menu under the 'File' dropdown. After selecting 'Shutdown', wait for the controller to finish imaging and the LEDs on the CPU go out (about 8 - 18 seconds) before turning off the disconnect. This will ensure you have a known good image when you power the controller back on.
The battery pack in the link looks correct but I've always used the 3HAC5105-1 pack made with NiCads, not NiMH. Not sure how the charging would be affected.
The NiCad packs require a 24hr 'ON' period to be assumed fully charged.
Okey, I'll try to find a NiCad battery instead of a Ni MH battery.
For this topic all i clear!
In addition, I have one problem with the connection to the FTP on controller, but I will prepare a new topic.
Thank You Skooter & Lemster68 for your help!