Repairing a Duracell portable power pack for my Stoker

[Professor Salt]

Has anyone had their portable power supply go bad and succesfully repaired it? Mine is no longer taking a charge. When I plug in to the AC adapter to charge it, it starts making long beeps. Does that sound familiar to anyone?

I called Duracell's customer care and they won't accept it for repair / return because it's past the 1 year warranty. They hinted that maybe a local hobby shop can fix it, but wouldn't elaborate on what they're fixing / replacing. Anyone know?

Amazon.com: Duracell DPP-300EP Powerpack 300 with Built-in 300-watt Inverter and 250 PSI Air Compressor, (Pack of 1): Automotive@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41R0XXrhHML.@@AMEPARAM@@41R0XXrhHML