Thanks for the Optima tip. I'd like to recount my experience in the hope of possibly helping others:
When I first realized my battery was dead, I ordered a Deltran plus battery charger / maintainer. It comes with a terminal adaptor that can be attached to the battery, making it easy to just plug it into the charger when needed. I then plugged the charger in figuring it would be fine in the morning.
WRONG. Next day, the battery was still dead. What I learned after reading the charger instructions (Duh), was that the charger will not work if the battery voltage is too low. Thinking that the battery was toast and wouldn't take a charge, I set about getting it replaced. Smart told me to call roadside and have the car towed in. I didn't like this idea much, as I was parked in an underground garage, and getting towed or even jumped would not be that easy due to space restrictions. Also, towing leaves the possibility of damaging the car, however small.
Smart would not give me a battery and let me switch it out myself, and buying one for $130 was foolish when the car is under warranty, so my next step was to get a battery somewhere else, if only to get the car into the shop. I didn't realize that a jump start would probably do the same. So, on New Years Day, I bought a Group 26R battery from Strauss Auto, which was nearby, and open. Cost, $50. I switched batteries and voila - the car sprang to life. Then I hooked up the removed dead battery to the charger and lo and behold - the charger indicated it was working (red light went steady, whereas it was flashing before).
I used the car that day with no problems. I had an appointment the next day for service, so I switched back to the original battery and drove it in to Smart. Smart agreed the battery was bad (voltage was still low, even after being on the charger overnight) and replaced it for free. Now I have an emergency battery that cost me $50 and a charger.
I learned a few things from this experience. One, if using a trickle charger you may need to disconnect the battery to get it to charge. Two, a 26R battery fits ok, but this one was a little loose under the bracket. Three, I am now an expert at removing and installing smart batteries
I'm going to make sure my lights and wipers are on OFF when not using the car. I hadn't used it for over two weeks when this trouble started. If I run into trouble again, I may invest in an Optima battery. I called Optima and spoke to a technician who wouldn't recommend an Optima for a Smart, but hinted that it might be possible. I'm sure now that it is, thanks to 24-42. Thanks for reading this and I hope it is helpful.