Power supply for desktop motherboard using Li ion battery

I would like to know whether it is possible to power the desktop using Li-ion battery. If so please do let me know how it is done. What i intend is to make the desktop PC portable using battery pack.

It would be very impractical to use a battery to power a normal desktop. For just the +12 V side a Deep cycle PbO battery might last 4 to 6 Hrs and that's a He** of a big battery. Of coarse this depends a lot on the GPU. My 9 cell Li-ion battery is rated at 65 WHrs - also only has 10.5 VDC out. A very Low end slim line Desktop normally has a 250 W psu. 3 $100 Li-ion batteries in parallel = about 30 -> 45 min run time (forgetting there output is only 10.8 V) You could build your own as frozenhead said, but it would be BIG and runtime would be short. You would buy individual cells, place them in series to give the desired voltage, and place a number of these in parrallel to yield the Wattage rating.

Also as frozenhead indicated you could run an inverter off of a battery. Again not to practical. If the Desktop only drew 50 Amps (+5V and +12V rails) - 50 amp/hr batteries - well you get the picture.