supplying power to a load and charging a battery as illustrated the system 100 includes a power source 102 a battery charging system 104 e g that may be part of a ups and a load 106 the power source 102 may be any of a variety of types of power source for example an ac to dc power supply that may be plugged into an ac wall outlet the load 106 is capable of drawing dc power from the power source 102 or a battery 112 and may be for example a modem connected to a telecommunications system the battery charging system 104 as illustrated includes a battery 112 a power monitoring subsystem 114 and current controlled charger with a switch 116 the battery 112 is a rechargeable battery of which many types exist and may be used the switch 116 is capable of adjusting the current supplied to the battery 112 and allows the battery to supply power to the load in the event of a failure of the power supply 102 for example the switch 116 is a pulse width modulated pwm switch capable of adjusting the amount of current provided to the battery 112 in accordance with an opening and closing duty cycle of the switch 116.