Studio 1749 Replacement Battery

I bought a Dell Studio 1749 in February 2010. Of course, now that it is out of warranty, I am having power trouble. Randomly, one day I got an error message saying my AC Adaptor was not compatible. But it is the adaptor that came with the computer, so I know that is wrong. Plus, I took the battery out and the computer runs off the adaptor, just at a slower pace. So I'm on to trying to replace the battery. However, my battery says it is manufacturer part # N856P. When I look up replacement batteries on Dell's website using my service tag, two batteries come up. One does not resemble my battery in any way shape or form, so it won't work. The other that does look like my battery says it is manufacturer part # N855P. It says it is for the Studio 1749, but the numbers don't match my current battery.

Does anyone know if the N855P is truly compatible with my computer? I'd hate to spend $135.99 for something that is not going to work. I'd become even more fed up with Dell than I already am.

Thanks!