A control system is designed or configured to control the state of charge of a battery or battery pack in a system containing a separate power source, which is separate from the battery or battery pack. In operation, the battery or battery pack is called upon to intermittently provide power for certain functions. The separate power source may be, for example, an AC electrical power source for a UPS or an engine of a vehicle such as a micro hybrid vehicle. The battery may be a nickel zinc aqueous battery. The control system may be designed or configured to implement one or more of the following functions: monitoring the state of charge of the battery or battery pack; directing rapid recharge of the battery or battery pack from the separate power source when the battery or battery pack is not performing its functions; and directing charge to fully charged level or a float charge level, which is different from the fully charged level, in response to operating conditions.