Harland Simon UPS recommends that if a system is not to be put into immediate service then the batteries within the system are charged within 6 months.
If batteries are left uncharged then they begin to self discharge themselves.
Therefore after about 10-12 months the batteries if left uncharged will probably be unserviceable.
A UPS can be powered up and with the inverter left switched off.
The rectifier will then maintain batteries until the system is ready for full service.
You can also order UPS’s with no batteries and order the batteries at a later date which can save money if the system is not to be put in to immediate service.