So I got the extended battery on Thursday evening and charged it with a charger from radioshack. On Friday I was happy with the performance of my extended battery and felt that it gave a significant advantage over the stock battery. So the Radioshack charger worked. or at least it worked well enough.
During the weekend I was at my partner's house where I left my OG Droid charger. I drained the Bionic full both Friday night and Saturday night and did not interrupt the charge until it reached 100%. That "100%" drained really quickly. One hour of streaming consumed 37% of the extended battery. So I'm now thinking that the OG Droid charger won't really fill up the extended battery.