Dell 2950 Battery Warning

Morning Guys,

I have two vSphere 4.1 hosts which host varying servers in our network. We monitor them using Nagios and do a Nagios storage check on them. The two servers since putting this check on them have gone red for:

"CRITICAL: Status of Battery on Controller 0 (Health State Not Good): The physical element is failing"

When I check within Vshpere it has marked a warning but says the battery is fully charged. The DRAC also has no mention of a failing battery.

Is this a red herring or should I be replacing the battery?

Thanks,

Matt