Note:21.9V is Pool Cleaner's battery voltage. NOT charger's voltage. Please Check For Compatibility With Your Unit. Thanks. Note: Rechargeable batteries typically last 1 to 3 years. If a battery is old or depleted,it may not charge,but this isn't necessarily the charger's fault. To determine if the charger is working,use a voltmeter. Compatible with listing item ASIN: B0D2K2HRFN - Cordless Pool Vacuum for Above Ground Pool: NexTrend Automatic Robotic Pool Cleaner Wall Floor Waterline Cleaning 180W Powerful Suction Last 150 Mins for Inground Swimming Pool up to 2,050 sq.ft Compatible with listing item ASIN: B0D45JLDQ9 - Cordless Robotic Pool Cleaner Automatic: NexTrend Pool Vacuum for above Ground Pool Wall Floor Waterline Cleaning 180W Powerful Suction Last 150 Mins Robot for Inground Swimming Pool up to 2050 sq.ft saschedross AC Adapter Replacement For NexTrend Model 60V Pro Blue 21.9V 7800mAh Li-ion Battery SAT-3P6S 180Wless Automatic Robotic Swimming Pool Vacuum Cleaner Power Supply Mains PSU