Generally i will make sure the battery is hooked up inside the UPS, then plug the UPS into the wall socket and hit the on button. I then let it charge for 24 hours. No hardware is hooked to the UPS until after the 24 hour period. After that you can hook everything up to the UPS.
If you have already hooked your hardware to the UPS, it does not mean it will fail when you need it. A couple of years ago i contracted to take care of a computer network system for a medium sized business. Of a 100 computers all were hooked up to small UPS under the desks and no one ever reset any of them. There were periods where the power was out for 10 to 15 minutes to the building. I was called in on a thursday late afternoon with 28 computers that would not restart. The reason was the UPS batteries were completely dead or the UPS's had not been reset, and no one knew how.A very hectic 3 hours and sending someone out to the local stores to buy 20 new UPS's convinced the management to invest in a building system UPS from the local power company. They figure they may have lost close to $100,000 in the 3 hours they were down, but there is no proof of that. Of course they blamed me even tho this was the first time they had a problem and i had signed a contract only 7 days before this happened. I tried telling them their system was antiquated but it fell on deaf ears. They started listening when the CEO called down from NY to find out what the problem was.
Anyway, i ramble. I had to hook up the UPS's without any charge period but sinde they had about 12 hours during the night to charge i had no problems with them. The good part about switching to a whole building UPS was they gave me all the small UPS's to get rid of. So now i have every electrical component in my house on UPS's, including my refrigerator. The reason for this is that here in florida we have short power outs and lightning strikes almost every day and sometimes many per day. I think this has saved my electric equipment from getting burned out. Before i had UPS's i had 5 computers burn up, 2 refrigerators die, a microwave oven die, 4 TV's quit working and 2 stereo system's that never worked again. All because of close lightning strikes that went thru the power lines and the telephone lines. Even had some lightning damage thru the Cable TV lines, so everything is on UPS's and surge protectors. I do plug surge protectors into the battery backup side of UPS's when i need more than one cable line surge protection, since the UPS's only come with one pair of connectors in them.
I hope this is more info than you need. Better for you to know what you can do than guess and hope it works.