A power tool energy source monitoring and control system comprising: an energy source input that accepts series connected voltages V1 and V2; a first voltage measurement point coupled to the energy source input; a second voltage measurement point coupled to the energy source input; a main power switch coupled to the energy source input and comprising a switch state control input; and a controller coupled to the first and second voltage measurement points and the main power switch; a memory coupled to the controller, the memory comprising: a cutoff threshold for disconnecting the series connected voltages V1 and V2 for stopping power tool operation; an operation threshold for connecting the series connected voltages V1 and V2 to allow power tool startup; a fading threshold for determining when voltages V1 and V2 are fading; and an energy source monitoring program operable to: measure the series connected voltage V1; measure the series connected voltage V2; determine when both V1 and V2 exceed the operation threshold 2. and responsively hold the main power switch in an 'ON' state using the switch state control input; determine when V1, V2, or both V1 and V2 fade below the fading threshold and responsively illuminate a warning indicator; and determine when V1, V2, or both V1 and V2 fade below the cutoff threshold for disconnecting V1 and V2 to stop power tool operation, and responsively hold the main power switch in an 'ON' state for an extension time using the switch state control input. an energy source input that accepts series connected voltages V1 and V2; a first voltage measurement point coupled to the energy source input; a second voltage measurement point coupled to the energy source input; a main power switch coupled to the energy source input and comprising a switch state control input; and a controller coupled to the first and second voltage measurement points and the main power switch; a memory coupled to the controller, the memory comprising: a cutoff threshold for disconnecting the series connected voltages V1 and V2 for stopping power tool operation; an operation threshold for connecting the series connected voltages V1 and V2 to allow power tool startup; a fading threshold for determining when voltages V1 and V2 are fading; and an energy source monitoring program operable to: measure the series connected voltage V1; measure the series connected voltage V2; determine when both V1 and V2 exceed the operation threshold 2. and responsively hold the main power switch in an 'ON' state using the switch state control input; determine when V1, V2, or both V1 and V2 fade below the fading threshold and responsively illuminate a warning indicator; and determine when V1, V2, or both V1 and V2 fade below the cutoff threshold for disconnecting V1 and V2 to stop power tool operation, and responsively hold the main power switch in an 'ON' state for an extension time using the switch state control input. a cutoff threshold for disconnecting the series connected voltages V1 and V2 for stopping power tool operation; an operation threshold for connecting the series connected voltages V1 and V2 to allow power tool startup; a fading threshold for determining when voltages V1 and V2 are fading; and an energy source monitoring program operable to: measure the series connected voltage V1; measure the series connected voltage V2; determine when both V1 and V2 exceed the operation threshold 2. and responsively hold the main power switch in an 'ON' state using the switch state control input; determine when V1, V2, or both V1 and V2 fade below the fading threshold and responsively illuminate a warning indicator; and determine when V1, V2, or both V1 and V2 fade below the cutoff threshold for disconnecting V1 and V2 to stop power tool operation, and responsively hold the main power switch in an 'ON' state for an extension time using the switch state control input. measure the series connected voltage V1; measure the series connected voltage V2; determine when both V1 and V2 exceed the operation threshold 2. and responsively hold the main power switch in an 'ON' state using the switch state control input; determine when V1, V2, or both V1 and V2 fade below the fading threshold and responsively illuminate a warning indicator; and determine when V1, V2, or both V1 and V2 fade below the cutoff threshold for disconnecting V1 and V2 to stop power tool operation, and