I am going to CDG on RER B but need to start at Gare de Lyon. Can/should I just use my RER ticket (I bought two when arriving at CDG, one for getting into Paris and one for return) to enter the metro (line 14 from Gare de Lyon to Chatalet) and then transfer onto RER B to de Gaulle? There's not an additional turnstyle I'll have to go through to swipe the RER ticket at Chatalet, just at Gare de Lyon and then when I exit at de Gualle? So, metro ticket on my Navigo Easy pass not needed at all in this situation?
I'm just trying to make sure I don't get stuck trying to exit the RER to enter the airport! Thanks!
Yes, your (2nd) RER ticket you bought at CDG upon arrival can be used from Gare de Lyon to CDG.
You can take purely RER trains from Gare de Lyon to CDG, avoiding any Metro transfers.
The common route would be RER A to Chatelet les Halles, transfer to RER B then ride till CDG 1 or CDG 2, whichever is better for you.
There shouldn't be any turnstiles/fare gates for your transfer at Chatelet les Halles between RER A and RER B. If I remember correctly, that transfer from RER A (westbound) to RER B (northbound) is on the same platform, just the other side, but I could be misremembering. At worst you'll have to ascend one floor via escalator find the RER B platform stairs/escalator and descend back onto the RER B northbound platform (direction Aeroport CDG 1/2 & Mitry-Claye).
You'll need your RER ticket to exit the train station at CDG though so be sure to hang onto it until you exit the train station at CDG inside Terminal 1 or Terminal 2 and are clearly no longer in the train station.
So, you shouldn't need that extra Metro ticket you have on your Navigo Easy pass.
When you're making your way to the Gare de Lyon RER A platform look for signs for directions Cergy le Haut / St. Germain-en-Laye / Poissy, which are the westbound RER A trains taking you towards Chatelet les Halles. I believe the Westbound and Eastbound platforms are separated so you'll want to get onto the correct side.