All batteries loose their ability to keep charge after sometime(especially in hot/warmer climate). Angalia cycle count ya your battery. Apple claim your computer should retain about 80% of its capacity after 1000cycle count.
If that's not the issue, angalia activity monitor what processes are running and consuming a lot of CPU power and deal with them accordingly, either uninstall them or tafuta alternatives. Out of curiosity unatumia Firefox with any extensions? It has been traditionally the biggest battery sipping application