The building I work in is actually a large datacenter that also has a little office space. One of the building managers mentioned that they would be replacing the batteries in the UPS shortly. I immediately stuck my hand up and said "I would gladly take some of the old batteries off of you hands". So, I have 4 batteries in the back of my car acting as ballast (100 Amp hours, 65 punds each).
Now, I've been giving some serious consideration to buying some solar panels and a charge regulator to keep them running. I'm also thinking about using the whole thing to power a number of receivers I have running 24x7 for audio streaming.
Sounds like the start of a fun project.