Can I use AA lithium batteries in my canon powershot A540 digital camera in place of AA alkaline bateries?

Yes, you can absolutely use lithium batteries in place of alkaline batteries. A WORD OF CAUTION*** Never mix lithium and alkaline!!

They would probably last longer.

Well i'm thinking you're using the normal AA alkaline batteries that you can buy easily in the market, that's what you use now. Lithium batteries are usually not available for a camera like that, they come like those "built in" batteries, for example for video cameras or for cordless telephones. What you can do is get AA "Nickel Metal Hydride" batteries, which are easily available in the market. They last longer than alkaline, and they are available in different MiliAmperes like 1300 ma, 1500 ma, 2100 ma. The higher you go, the more time it takes to charge the batteries, and the more time they work. Give them a try.

That shouldn't matter. I have a Nikon Coolpix 3 that uses two AA batteries. It can use alkaline just fine. I put rechargable NiMH in it and they last for MONTHS with no problems.

yes u can use it