Many people are discovering Lithium Ion batteries as a replacement for lead-acid types.  At 1/3 the weight per unit of storage, they're much better for go-kits a other portable gear, and some of their electrical characteristics make them compelling options.  Some companies manufacture drop-in replacements for standard lead-acid battery sizes & styles, making it effortless to use them.  They're much more expensive, though, so they're hard to justify in a fixed installation.  Still, if you want the best...I wouldn't mind having this 700 lb. bad boy supplying my UPS! :-)