Reed Muse 3C turntable

exlibris, have you considered Lithium Polymer or Lithium Ion (Li-po / Li-ion)? I don't recall you mentioned battery tech of your existing 12v. Perhaps 2 batteries, one on charge when the other is in use?

Thank you for the recommendations I will investigate.  Details on the battery I have can be found by clicking the link in the message I posted above on 08/28/2015.

I looked into the various lithium-based batteries and they appear to be an excellent option.
The only hesitation I have is the protection circuitry that they contain.  
"They require protection from being over charged and discharged too far. In addition to this, they need to have the current maintained within safe limits. Accordingly one lithium ion battery disadvantage is that they require protection circuitry incorporated to ensure they are kept within their safe operating limits."
I'm just wondering if any of this circuitry can produce noise which could lead to speed fluctuations in the turntable(?)

Any owners in EU?

I've since added a second battery (in series) and that produces 24v.  I then use a linear voltage regulator (with adjustment knob and digital readout) to deliver a steady, consistent, and exact number of volts to the table.  The motors can run on anything between 10.8 to 13.2 and right now I'm delivering 12.9.  The speed fluctuation on this table is vanishingly low according the measurements I see on my "Platter Speed" app.  More importantly, music simply sounds right, in a matter-of-fact kind of way.