[Test-Equipment] CORRECT BATTERY VOLTAGE AND TYPE FOR HP3586A SLA

[J.Byers]

Does anyone know the battery voltage (in PSU regulator control board, upper RHS slot of instrument motherboard) so a replacement can be fitted to a HP3586A Selective Level Meter ?
Battery marked GE 8218  and  1420-0251, which probably is HP part number... no doubt a NiCd type.

The unit is currently giving an 'Error 8' at self test start up and I hope this dead battery is the reason

Thank you 
J.Byers