KWA M4S lipo battery?
 

I currently own a kwa M4S it comes stock with a Intellect 8.4v 1600mah battery. I want to upgrade to a LiPo battery, does anyone have any suggestion for what voltage or mah I should use? And also is there a company that has better quality then others?

Thanks

elite airsoft batteries
https://www.eliteairsoftbatteries.com/

7.4v lipo, any mah

7.4vs are equivalent to a 9.6 NIMH which your gun will be able to run most likely

KWA should be okay on 11.1v, at least for a while. A good site for inexpensive batteries is hobbyking.com, there are a million to go through. When you're looking on the site, find a pack with the same or similar dimensions to your current battery. A good brand to stick to would be Turnigy Nano-tech, but they're all decent.
When you're looking on the site, they won't say voltages but an S-count. The number before the S is the amount of cells in that particular pack. 2S = 7.4V, 3S = 11.1V.
Remember to get a lipo alarm and lipo-capable charger! Check out the lipo sticky somewhere around here for safety concerns, they are safe as long as you're not a derp!

Give this a read first, pretty much everything you need to know about LiPo;
http://www.airsoftcanada.com/showthread.php?t=99899