I would plan to replace it accordingly. The message may have gone away for now if the battery went through a recent relearn cycle where it was discharged and recharged which may have temporarily cleared the error state. But nonetheless, it will most likely fail soon.   Let me know if you need any replacement procedures that i can help with. It is a simple customer replaceable part. 
A PE 2950 was displaying a "W1228 ROMB battery < 24 hrs" warning message in amber on the lcd display. In the past when we saw the warning on other servers we replaced the ROM B battery and that resolved the issue. In this case though, it was taking a few days to move things off of the system so we could replace the battery. After 8 or 10 days the display returned to normal. Does this indicate the battery has charged to a normal level and doesn't need to be replaced at this time or should we continue with the plan to replace it?
W1228 ROB B Battery Warning