Not enough info -
What kind of juices, how much nic, what PG/VG - high nic is harsh. Nic is harshest in 100% PG
juice. And heat makes it a even harsher. Heat can make lower nic harsher too. i recommend 70pg/30vg and standard resistance atomizers or cartos to start. And I assuming you got the awful tasting primer off the attys before inhaling.
So - what ohms are you
vaping them on - sometimes low resistance attys come with Rivas and those are hotter. The reason many people buy Rivas is because they want to use low resistance attys and cartos and get hotter hits. I don;t really think that is the best thing for someone who is starting out. if your hits are too hot then get standard resistance attys or cartos for now.
510 to 901 adapter is to go from a 510 battery to a 901 atomizer. If you were trying to use to use it the opposite way then that will not work. In that case you need a 901 to 510 adapter
And where did you buy from? A number of us got Riva 510s at Liberty-Flights.com with no problem.
if your batteries are failing then maybe your charging cable or charger are defective. And when you screw them in to charge you need to first make sure the threaded end is totally clean and dry and screw it into the charger just enough for the light on the charging cable to stay red (means it's charging). And it should be a Riva charger, not any other cable. And it needs its own motherboard USB slot on a PC or a proper AC to USB with enough amperage, like the one sold for it or any 500mA 5v AC to USB adapter (that is enough to charge ONE battery)