Need help: 300E won't start

[McLoffs]

Hi everyone. After it had been sitting for a couple of weeks, yesterday my 300E wouldn't start. Turned the key, got unpleasant clicking noises from the engine compartment, and nothing happened. Thinking it was the battery I pulled it and put it on the charger overnight.

After the charger indicated the battery was ready, I reinstalled it this morning and had the same thing happen -- turn key, unpleasant clicking noises, car doesn't start.

All of the electrical accessories work fine with the charged battery; it's just that the car won't start. I also tried jumping it but that didn't work either. I suspect the battery is good enough to run accessories but not powerful enough to start the car, so I'm thinking a new battery is in order. Any thoughts/suggestions before I go out to try and find a battery on a Sunday?

Thanks,
Mike