Use this smart battery charger LTC4100EG charge controller from Linear Technology to monitor the state of your batteries. With an output that has a voltage of 3.5 to 26 V, this is power management at its best. Its output produces a current of 4000(Max) mA. This battery gauge has an operating temperature range of -40 °C to 85 °C. This device has a minimum operating supply voltage of 3 V and a maximum of 5.5 V.