First, my condolences to you, Kingharold. So sorry to learn of your recent bereavement. Sounds like your wife was a wonderful person.
Second, having been the first to recommend substitution of an Optima auto battery for the $1200 Clearaudio battery supply, I would point out that Optima batteries are sealed and do not vent any noxious gases, ever. Noromance makes a valid point that an unloaded car battery will make up to 14V when fully charged. Whether that would damage the DC motor or not is definitely worth worrying about, but I don't think the danger would be much ameliorated by an in-line fuse. A fuse senses current, not over-voltage. One would have to determine whether the load presented by the motor will pull down the voltage to an acceptable range around 12V, and if not, and if one were really determined to go this route, one could calculate the current draw necessary to bring down the voltage to the desired range and insert an appropriate resistor in series. (I really doubt it would be necessary but worth evaluating.) Optima make a sophisticated trickle charger specifically designed for use with their batteries. I recommend that too. I have been using Optima batteries for 20-25 years on one or another classic car in my closed garage, with nary a problem. I am sure some of the smaller size batteries discussed here would also work, but there you would have to worry about its maintaining output voltage over the course of a long listening session, because in my experience battery-powered audio gear does not sound good with charger in operation. Smaller batteries tend to have less capacity to store current. And finally, I did find that capacitance in parallel with the battery output did audibly improve sonics, for whatever reason, in my one long term experience with battery power. I used a couple thousand microfarads in the form of 16V electrolytics wired in parallel.
But third, I also like what Bill said about using a regulated linear power supply. I am sure you can buy a good one off the shelf for less than half of $1200.
