Have a read through this:
http://p8ntballer-forums.com/threads/what-battery-are-you-using-in-your-eclipse-marker.106174/
It's about eclipse guns but is the same for any brand.
Solenoids need a good level of power to function, and 'better' batteries are more consistent with the output, keeping the power level up through the operating life
Individual players and guns will have different experiences and may work perfectly with a Duracell or may not get any joy with anything but a paintball specific brand
It's probably mentioned in the thread but Babs on eBay is a popular seller.
Personally I'll buy procell in bulk or duracells from a supermarket if I'm out.
A teammate who will remain nameless and requires confidentiality as far as his wife is concerned has had gun issues for some time, sending it back and forth for servicing and 'did not buy a new gun at paintfest with cash from a paintball account that the wife does not know about'
The gun that he didn't buy didn't end up with the same problem
Quick visit to tech support and both his real and imaginary guns were fixed by a twin pack of paintball batteries