@skematica I had a "battery needs servicing" warning on my 2008 MacBook Pro when it was running Mountain Lion, Mavrix & Yosemite. But when I updated ot to El Crapitan after fitting a fast SSD in place of the HDD, the warning vanished, never to be seen again.
The first thing to try is turn it off & back on again. If that doesn't work, download & run the latest Combo Updater for your OS.