PowerWalker VFD 600 APFC - Manual (Page 6)

3. Charging
This unit is shipped from the factory with its internal battery fully charged.
However, some energy may be lost during shipping, so the battery should
be recharged before using it. Plug the unit into an appropriate power supply,
then switch on UPS and allow the UPS to charge fully by leaving it plugged
in for at least 8-10 hours with no load (no electrical devices such as
computers, monitors, etc.) connected.