Steam iron may too violent a load, and could have damaged the UPS, so you'd be lucky to have got away with that if you did.
Unless, of course, your iron is less than 400 or 500W. They are usually range to about 800W, the limit of a 1100VA unit and well past that of a slightly used one.
Anyway, if it is still running it seems to be alive, mostly. Another load you can try is a monitor with input cables disconnected and set to full brightness. The backlight should activate and run at full power with the 'no input cable' sign displayed, which you can disregard. If you have a printer you can add that as well, and test both power on and backup.
FWIW the battery on my APC is toast too, it barely lasts 5 minutes at mild load of 300W and needs everything to be switched on only when mains is present as it can't handle the startup surge of my 600W+ system. And it's about two years old - so you may also need a new battery.