Possibly Dumb Question re:Battery as a power supply

" I assume you are not married? " 
I was married up until July first of this year when Mary, my wife of fifty-one years, passed away.  Even before that I could get away with many things other audiophiles can't because my wife was a true audiophile and reproduced music lover herself.  At her funeral a long time friend (40 years +) who has been a audio professional all his adult life commented about how unusual Mary was that she understood the technical terms of sound reproduction and could intelligently discuss them.   When I told Mary I wanted to add two eighteen cubic foot sub woofers (Bill Fitzmaurice designed 25 Hz quarter wave corner horns) to the system in our den she just said, "OK, but let's make sure they look good."  She spent hours helping my apply blonde Burmese Teak veneer to the Baltic birch cabinets.

@kingharold Thanks for relating the stories about your wife. That is a rare occurence I would say! Though my wife doesn't share my same enthusiasm she gives me a lot of leeway; but if she didn't I would take it! I know we have to compromise but I worked for it, I earned it and I can think of a lot of other things worse than enjoying music. WAF be damned!

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.

There is a complete battery operated turntable motor and power supply on US Audiomart https://www.usaudiomart.com/details/649783098-turntable-motor-with-battery-power-supply/

That might work well for you.

No problem, charge away! Just make sure the battery is well ventilated. Lead acid batteries make hydrogen gas which is explosive. Enclosing it in a cabinet is a terrible idea.