I have a Riva 901 and I'm diggin' it hard. I had a problem like this and I ended up finding out it was due to the wall outlet adapter that's separate from the USB charging cord. I plugged the battery into the USB charger only, then plugged the USB end into the PC and let it charge overnight... BAM, fixed. Contacted support and now a new wall charging adapter is on the way.
Although I've also seen a few posts concerning Riva battery connections not making correct contact, so that may be it as well. There's a
thread on here that shows how to
barely lift the battery-end connection up. I haven't had that problem yet, but it seemed to help quite a few people. Anybody out there have the link to post here (I'd search for it but I'm chasing a screaming, pooping 2 yrs.-old atm).
Are the threads on the battery side allowing the atomizer to go all the way down to make connection? Is the charger's red light turning to green signaling the end of the charge?
I don't have much experience with mine yet but I use it like a whipped mule. Hopefully somebody with more experience will chime in here. And if all else fails, I'd contact the supplier's support. Every model of e-cig made is known to have a few bad pieces in the bunches.
Good luck in finding out what's going on with your 901!