Controlling battery states of charge in systems having separate power sources

A controller for controlling the state of charge of one or more nickel-zinc batteries in a battery pack for a system having (a) a separate power source working in conjunction with the battery pack and (b) a full charge mode and a float charge mode, the controller comprising:

• a communications interface for communicating with an alternator and/or an engine control unit;
• and
• logic for
• (i) determining that the state of charge of the one or more nickel-zinc batteries in the battery pack is below a defined level associated with the full charge mode;
• (ii) while in the full charge mode, applying charge to the battery pack at a first voltage to charge the one or more nickel-zinc batteries of the battery pack to a fully charged state, wherein the charge to the fully charged state is provided from the separate power source;
• and
• (iii) subsequently, while operating the system in the float charge mode, applying charge to the battery pack at a second voltage to maintain the one or more nickel-zinc batteries of the battery pack at a float charged state, wherein the charge to the float charge state is provided from the separate power source, and wherein the magnitude of the second voltage is below the magnitude of the first voltage.