I highly recommend the E-Power 14650. Its a really nice 3.7V that is a 510. I use it mostly with 1.7ohm LR "Ressurector" cartos and also have a HH .357 atty for dripping and both hit like a beast! Its a really affordable mod and ALL parts of the unit can be replaced which is really nice and keeps costs down.
Another plus is that it uses non-proprietary batteries which is great cause instead of paying close to 20 bucks for a whole new battery unit when your riva quits, you just need to buy a new seperate battery. You can get the 14650 batteries for 4-5 bucks and the "High-Drains" for 7-8 bucks. I have both and they both work really well and they last a long time! About a whole day on one battery.
Another plus is that the switch is regulated so you get a really consistant vape, instead of really trailing off when the battery is almost dead on a lot of other units. Some say it is NOT regulated, but it def is. Ive tested it and at full battery I was at 3.75v on the dot and with a battery that was almost completely dead the absolutely lowest reading Ive gotten was at 3.68v. Thats pretty darn good. Also, many people were complaining about the rubber button on the switch bc it would stop working, get stuck inside, etc. And that def was true, it was a pain, but they just came out with a new plastic button for the switch and its MUCHH better. And if really needed, you can just buy a completely new switch assembly for under 10 bucks.
If your looking to get one I would def get it from Crystal Clear Vaping. Ive looked around and they def give you the best bang for your buck. For $57 bucks, you get the E-Power kit, comes with 2 batteries, the new plastic button switch, cone, 2 510 attys, 5 cartidges, wall charger. Thats the whole kit. But where you get an awesome value is this. CCV throws in a FREE 5-Pack of the 1.7ohm LR "Ressurector" cartomizers (which totally kick ....) and they also throw in a FREE 30ml bottle of an
E-Juice of your choice. (I got the Black & Mild and I really like it) If you add it up thats $23 in free extras!! And to top it off they give you free priority shipping. It really is an awesome deal.
Plus, put in coupon code "ecf5off" and get 5% off.
I also recommend buying another pack of cartomizers, either the ressurectors or the Boges, because he throws in a free syringe and needle with every cartomizer pack purchase!
The guy at CCV is a really good guy as well and extremely helpful. His customer service really is top notch.
I hope all this helped!
Rob