Need a little help with UPS as inverters

[AzurA86]

i read about turning a UPS to an inverter
i hooked a 20W PL screw light such as this one
http://174.143.168.95/ba/image-websi...ulbs--SM15.jpg
and turned it on using the battery on the UPS-7AH 12V
its working great for 5 min and then it turns it self off, the battery still good cause all i do is turn it back on and it works for another 5 min
why is it happening ?
the goal is hooking the UPS on my boat as an inverters just to light it up with some 220v light
i have another UPS here which has 2X12V batteries which gives it 24v to work, the thing is , on that UPS it works great, tested it for 30 min and it ran just fine, theres isnt much difference between them then the VA/W, one is 600VA and the other is 1000VA, both of them output modified sinewave, both are from IPPON, so what could be wrong ?

[theAnonymous1]

Are you aware they make 12V 20W CFL's?

http://www.amazon.com/12V-Watt-Compa.../dp/B002M41X6M
http://www.onsolar.co.uk/12V-20W-CFL.shtml

Seems like it would be a lot more efficient and simple to just buy one and ditch the UPS.

[AzurA86]

Originally Posted by theAnonymous1

Are you aware they make 12V 20W CFL's?

Amazon.com: 12V DC 20 Watt Compact Fluorescent Bulb - Spiral: Home Improvement
OnSolar.co.uk 12 volt dc 20w low energy saving cfl lighting and bulbs

Seems like it would be a lot more efficient and simple to just buy one and ditch the UPS.

im aware of that, in fact i already tried that, the reason im switching to 220v is that these are a lot cheper
besides, its always good to have 220v on a boat, not for just lights.