A battery system , comprising: - a first battery configured to be coupled to an electrical system , wherein the first battery comprises a first battery chemistry; - a second battery coupled in parallel with the first battery , wherein the second battery comprises a second battery chemistry that has a higher coulombic efficiency than the first battery chemistry - a bi-stable relay configured to selectively couple the second battery to the electrical system , and wherein the bi-stable relay is configured to: - couple the second battery to the electrical system during regenerative braking to enable the second battery to capture a majority of power generated during regenerative braking; - maintain a coupling of the second battery to the electrical system after a vehicle transitions from a key-on position to a key-off position for a predetermined amount of time or while a voltage of the second battery is greater than or equal to a predetermined voltage; and - decouple the second battery from the electrical system after the vehicle transitions from the key-on position to the key-off position and when the predetermined amount of time has passed or when the voltage of the second battery is less than the predetermined voltage resulting in a long key-off position, and - an alternator configured to output a first voltage during regenerative braking to charge the second battery and to output a second voltage otherwise, wherein the first voltage is higher than the second voltage. - a first battery configured to be coupled to an electrical system , wherein the first battery comprises a first battery chemistry; - a second battery coupled in parallel with the first battery , wherein the second battery comprises a second battery chemistry that has a higher coulombic efficiency than the first battery chemistry - a bi-stable relay configured to selectively couple the second battery to the electrical system , and wherein the bi-stable relay is configured to: - couple the second battery to the electrical system during regenerative braking to enable the second battery to capture a majority of power generated during regenerative braking; - maintain a coupling of the second battery to the electrical system after a vehicle transitions from a key-on position to a key-off position for a predetermined amount of time or while a voltage of the second battery is greater than or equal to a predetermined voltage; and - decouple the second battery from the electrical system after the vehicle transitions from the key-on position to the key-off position and when the predetermined amount of time has passed or when the voltage of the second battery is less than the predetermined voltage resulting in a long key-off position, and - couple the second battery to the electrical system during regenerative braking to enable the second battery to capture a majority of power generated during regenerative braking; - maintain a coupling of the second battery to the electrical system after a vehicle transitions from a key-on position to a key-off position for a predetermined amount of time or while a voltage of the second battery is greater than or equal to a predetermined voltage; and - decouple the second battery from the electrical system after the vehicle transitions from the key-on position to the key-off position and when the predetermined amount of time has passed or when the voltage of the second battery is less than the predetermined voltage resulting in a long key-off position, and - an alternator configured to output a first voltage during regenerative braking to charge the second battery and to output a second voltage otherwise, wherein the first voltage is higher than the second voltage. <EOS>