@Bruce Johnston welcome to Electronics Point!
To expand just a little on Dave's reply... you first need to convert the variable battery voltage (12.6 to 14.5 V DC) to a higher DC voltage that can then be regulated down to your desired 12 V DC. A switch-mode power supply (SMPS) is typically the method used to do this. The SMPS uses the raw DC voltage from the battery to drive a power oscillator that stores electrical energy in between cycles of the magnetic field of an inductor. The cycles are not necessarily sinusoidal, but that is beyond the scope of this comment.
The cyclic electrical energy stored in the magnetic field of the inductor is retrieved every cycle, rectified, filtered, and regulated down to the desired 12 V DC. This latter operation leads to the term "buck converter" meaning part of the input voltage is "bucked" to a lower output voltage. However, the voltage obtained from the magnetic field stored in an inductor very much depends on how rapidly the magnetic field is collapsed (circuit design) to retrieve electrical energy. It is therefore possible (and practical) to obtain more output voltage than the input voltage by using a "boost converter" SMPS.
SMPS technology didn't exist in a practical form until the development of low-loss, high-frequency, switching transistors, which today are typically MOSFETs switching at high kilohertz to low megahertz speeds, limited more by inductor core loss characteristics than MOSFET switching performance. The market boomed in the waning years of the previous century and is now flooded with very affordable, inexpensive, Asian products. Or, since this IS a forum for DIY hobbyists, you can "roll yer own" and learn about this fascinating technology at the same time. All the essential components are readily available online, as are "monkey see, monkey do" instructions. Make Google your best friend to explore the possibilities, but most of all have fun!
