My 5 REO's are the backbone of my vapocalypse stash. I am guessing you have one of the minis?thank you guys so much for the helpful info. I picked up another mod today and I'm also looking at getting a regulated something squonky (so many products to check out) so I can have one of those too. I did get the efests, though I'm not confident about those. I may also get the keeppower and see how they do. I love my Reo and don't want to stop using it for lack of batteries. Oh the irony, my mod can survive being run over by a vehicle, but still can't work because there's no batteries for it. Totally silly. I'm just happy there are some reasonable alternatives to consider (though likely not as durable. hopefully that won't have to be tested). Most appreciated everyone.
If you want a regulated I have really enjoyed the Pulse BF 80w/90w. With the kit you also get a nice squonk atty for it.
For unregulated have a look at the Athena.
Both can be picked up relatively cheaply (particularly compared to the price of a REO back in the day). I would also tell you to keep your eye on the classified. Used REOs come up occasionally. A Standard REO or a LP Standard REO would keep you in a REO but using 18650s.