Try to dismantle the battery box. Measure the voltage of each battery cell. Some cells may have zero or low voltage, nominal value should be 1.25 V if not completely discharged. These cells may be replaced with new ones bought individually or in fours from a supplier. They will have to be soldered in place.
Or they may be revitalised by shocking energy into them, that is by using a large capacitor (such as 50 000 microfarad) charged to say 15 volts as energy source. The shocking will in case remedy the cell by burning off some "metal beard hairs" that may have grown up between the electrodes over the time.
Bror, the retired repair man having oceans of time., August 2009
