[ ProLiant ML350 G5 ] Smart Array E200i battery failure without 'replace' notice?

We have a ProLiant ML350 G5 server which displays battery failed.  Please see attached jpg.

Read from other user's message with same issue . But it noticed to replace battery.

http://h30499.www3.hp.com/t5/ProLiant-Servers-ML-DL-SL/ProLiant-ML350-G5-Smart-Array-E200i-battery-failure/td-p/4668811#.UgyiN9KnjTq

But my server doesn't show replaced.  Should I buy battery to replace it? or Just ignore it?  Please advise.