Took my 2003 C240 with 20K miles on it to the dealer for A service. Car was running fine. Dealer says battery did not pass a test, but I told him not to replace because I knew I could get it done cheaper elsewhere.

On the way home, it ran rough at a stop light and hesitated when I got on the gas to pull away from the light. I thought it was going to die in the intersection. I thought, maybe bad gas so I filled it up with premium and drove it some more, still did the same thing. Finally, three days later, the computer codes. The diag by dealer says "to lean on right bank". What I want to know is this:

1. Is this a common problem and what could be issue?
2. Does anyone know of a good repair shop in the San Antonio/Austin area? I don't want the fix done at the dealer cuz it will cost a fortune.

Thanks in advance for any help.