Rechargeable batteries have a lifespan of 1 to 3 years. If a battery is aged or drained, it may not be able to recharge, although the charger may not be at fault. If unsure if the battery or charger is malfunctioning, use a voltmeter to test the charger's performance.
(Note: 36V is battery's voltage. NOT charger's voltage. Please Check For Compatibility With Your Unit. Thanks.)