macbook pro – 2008 MAC BOOKBOTTOM , A1278. 2-PIECE BOTTOM

I found a 13″ Mac Book. I don’t have a power cord, so I am not able to turn it on. It is a Model A1278. Rated 16.5V — 3.65A Max. The date on the case is 2008. It has a bottom case that appears to have two halves. There is also a small spring-loaded tab on the bottom case. I’m trying to find whatever information anyone can provide concerning the unusual bottom case for this laptop. Thank you!