Cannot find matching laptop battery for Inspiron 559

I have an inspiron 5559 laptop which is 1.4 years old. I have replaced my ram cards with HyperX 16Gb kit and then I realise fast battery draw. Anyway after 1 month from the upgrade battery status went excellent  to normal. now its POOR. I want to buy a new battery. I couldnt find any original battery from local stores hence I live in Sri Lanka.

1. Can anyone tell me what is the correct laptop battery for my laptop.? 
2. How to find it? and where?
3. How can I know it is a genuine one when I'm buying it? 

PS: many of the sites says it's Li-Ion battery but when I save the battery details of my system into html file it says Li-Po..