The P400 Smart Array controller in my HP DL380G5 is indicating:

Battery Status: Failed, Replace Battery 1

in the System Management Homepage. Also the IML indicates:

POST Error: 1794-Drive Array - Array Accelerator Battery Charge Low

I do have several replacement batteries (actually, several controllers including batteries) lying around at work but never had to actually replace one. I am wondering if the battery replacement (swap) could be done hot or if I need to take down my server to do the battery replacement.

I have replaced other spare parts like fans and drives before and all those can be replaced hot. I just don't know about the battery of the P400 Smart Array controller. Any help would be appreciated.

EDIT1

For those interested: straight from the horse's mouth:

With thanks to Frands Hansen pointing it out here.

EDIT2

In the end I did just power down, to be on the safe side and because the manual says so, and replace the battery. Couldn't be easier. Unplugged the old one of the end of the cable (not the end connected to the controller) and reconnected a spare one. The replaced battery is now in the server for about an hour and currently (still) recharging. I'm assuming all will end wel.