Motorcycle Repair: battery, battery tender, side car

Question
I have a '97 Sportster that started life as an 883. I got a side car for my disabled son to ride in and had the motor bored out to 1200 to better carry the added load. The side car has a radio in it and the clock is always on; if I don't keep the battery tender on it the battery becomes too weak to start the motor. Last weak I inadvertently left the start switch on and the battery tender off, and the battery was completely dead. I reconnected the battery tender for a week, but now when I try to start up I just get a fast clicking sound. Is my battery destroyed? Is it possible that the starter or some other OEM item isn't suitable for the 1200? Is there a better charger that I can get to get me started and will the battery come back to life? Is it damaging to keep the battery tender on all the time?
Appreciate your answers. Thanks in advance.  

Answer
First, the battery tender will not hurt the battery if you leave it plugged in all the time, as long as its the type that shuts off when the battery is charged.
If you left the key switch on you need to check the coil to make sure you didnt burn it up. That is what usually happens. leaving the key on will completly discharge the battery, so you need a charger to charge it. the battery tender doesnt put out enough amps to go from a dead battery to completly charged.
Your starter is fine for your bike. The 1200 starter and the 883 starter are the same.
Good luck and happy riding
Mike