Mercedes E55AMG (2005) failed to start couple of times

Question

About couple of months back my E55 didn't start. I called AAA to tow. Before help arrived after 15 mts I tried and was able to start the engine. AAA guy came and tried and it started without any problem. I was using the car without any issues. About 10 days back again it didn't start and called AAA. AAA person came and car started without any problem. He did a battery test and it passed. Now engine starts without any issue and I don't know, when it will give trouble. Engine never fails during the drive.
One more observation-After this problem, engine light comes and it goes away after driving 10 mts. Could you please let me know what will be the problem?
Thanks
/Sridhar