A 12 volt automotive battery system includes a first battery coupled to an electrical system, in which the first battery include a first battery chemistry, and a second battery coupled in parallel with the first battery and selectively coupled to the electrical system via a first switch, in which the second battery includes a second battery chemistry that has a higher coulombic efficiency than the first battery chemistry. The first switch couples the second battery to the electrical system during regenerative braking to enable the second battery to capture a majority of the power generated during regenerative braking. The 12 volt automotive battery system further includes a variable voltage alternator that outputs a first voltage during regenerative braking to charge the second battery and a second voltage otherwise, in which the first voltage is higher than the second voltage.