@phoenixengr, glad to see you join in this discussion, your expertise is greatly appreciated!
BTW, I’ve been using the Teres battery power supply on my turntable for more than 15 years without any problem and only replaced the SLA battery about 5 years ago. The SLA battery will charge up to 13.8V if not in use.
I found an internal image on the Hifitest.de review of Clearaudio smart power 12V. https://www.hifitest.de/images/testbilder/big/clearaudio-smart-power-12v-hifi-sonstiges-57224.jpg
I can clearly see a LM317T regulator chip in the circuit, I could be wrong, but I think the LM317T is to regulate the output voltage while the 19V wall wart charging the NiMh battery and at the same time supply power to the turntable. In pure battery mode, I not sure if the regulator chip is in circuit or not. Without a schematic, just take a wild guess.
The user manual also warn that if connect the 19V wall wart directly to the turntable instead of the OEM 12V wall wart can seriously damage the turntable!
Since we don’t know what is the highest voltage the turntable can safely take, and OP also concerned if 14V will be too high for his turntable, that’s why I came out the " overthinking " dumb idea of install a simple voltage regulator between the battery and turntable.