replacement battery for C710-2847

Purchased a replacement battery for my C710-2847. Came in, was a different shape than the existing one. Existing one is about 3/4" thick (flat), while replacement is larger and triangle shaped. Fits, but I can't get it to charge up. When new battery in place, and unit plugged into ac power, no battery icon shows.

Any idea where I can purchase a flat replacement (AL12B32) 14.8vdc 2500 mah. Or was the one I purchased just so dead I couldn't get it to charge? Should I try another triangular one?