The energy stored in your UPS is 7 Amp Hours (battery capacity). It will operate on battery for 3 minites at full load, or 20 minites at no load, (just the inverter) I expect that it will operate for a little more than 15 minites while running your lights.

http://www.ehow.com/how_7640599_calculate-ups-output.html

You would do better with a marine battery and DC lighting...

You could just run it off a car nearby with a little plug in adapter and extension cord...$24

http://www.ecrater.com/p/11564303/12v-dc-to-220v-110vac-75w?gps=1

You could use one of these portable jump starters for the car, with the adapter...This one has 12Ah, should last all day...

http://www.autoanything.com/electrical-components/65A5290A0A0.aspx?kc=ffproduct

The LED lighting probably runs on low voltage DC, with small transformers to make it run off of house current.

For your display, you might try to wire the displays directly to a battery, bypassing the transformers. They should run a long time that way.

Explain to your customers that you are using battery power to run the lights. They may be impressed and want to do the same!

You may open up a larger market than you first imagined.

The DC direct method would be most efficient if you can do it that way.

The typical UPS is not designed to be deeply discharged and then recharged multiple times. The charging circuits frequently fail, or charge the battery too fast and the battery fails, or both. There's another recent thread about this on CR4 discussing adding additional batteries to the UPS to make it run the equipment longer. The overall consensus is that is a very bad idea.

You would be much better off with a large (Group 24, 27, 31, even larger?) deep cycle AGM sealed 12V battery and a small inverter that just meets your AC power demand. Don't get a huge inverter because that will waste energy on fans and ampacity you don't necessarily need.

The AGM batteries are spill proof and do not emit gasses under discharge, so the mall should not be against this battery type. It's probably safer than the sealed lead-acid battery in the UPS anyway.

This way instead of 7Ah battery, you can have 70-130Ah in a single battery that will have a much longer life span going through the multiple discharge-charge cycles you will have. If you need a longer run time than one battery would give you - more like 150-260 minutes at the load you stated, you could always parallel (not series!!!!) two or more batteries.

Sure, this is bigger and heavier than just a UPS but it will give you many more hours run time than the UPS.

One issue with your plan is that a quality charging system will take about as long to charge the batteries as they took to discharge or maybe even longer. So you may end up needing two batteries to rotate for each mall cart inverter so the used batteries can have the proper charge time.

Cheap Charger = Early Battery Death

84 watt-hours. (= 0.084 kwh)

Almost. The efficiency rating of greater than 80% implies to me that one should expect no more than (0.084*0.8) kwh ≈ 0.067 kwh.

have you thought about a very small generator?

While there may be plenty of power many UPSs are limited in time that they can operate. That said I ran 60 watt bulb for a couple days during a hurricane and had no problems. It did give out an annoying beep every minute.

For the UPS units that I use as inverters I go into the pc board and carefully drill out the top of the beeper and remove the little piece of metal in there. That leaves the beeper in the circuit, but it is silent.

With 67 Watt hours of total energy available with a fully charged battery, I think you should know your load circuitry a little better than having a 15 watt ± 5 watt tolerance. This will mean that your display will work for 6 or 3 hours of continuous operation. If this arcade is open for only two or three hours then you'll have no problem displaying these lamps with this supply. However, if I was a potential customer at this arcade I would never buy a product intended to use local power grid voltage unless it was using local grid voltages. Sell something that doesn't use electricity or pay for a kiosk with electricity.