[Renate]

Most Onyx seem to use thin (thinner than common) batteries, 2.5 mm.
Battery numbers are only dimensions. CLP2575147 = 2.5 mm x 75 mm x 147 mm.
Loose wires like that are dangerous. They cheaped out even though there is a connector on the PCB.
The white wire is probably a 10 k NTC thermistor to the black wire.
When you replace the battery double-check that the temperature reads something sane in a utility (like my UsbMode.apk in the sig).