What do these Battery Specifications mean?
"Standby use: 6.8V - 8.9V   "



It means you made a typo error.
Standby use: 6.8V - 6.9V or 6.85/3=2.28V/cell at std temp=20'C


 Cycle Use= Charge-discharge voltage per cell is the std way to specify multi-cell batteries.

Normally battery chargers for SLA's must be temperature compensated to achieve rated life of 500 charge cycles.  There is a float voltage range and a charge voltage range which can be discharged in this range as well so it is called CYCLE USE.

Much more can be learned by getting OEM specs not reading stuff on Ebay or Amazon
http://sa.tipa.eu/datasheet/04250135-datasheet-en.pdf