Resurrecting dead DJI batteries

[Mechanicus_95]

I recently bought a DJI Phantom 4 pro. Have three batteries but only 1 works others don't charge. Looks like they were left uncharged for about a year. Any recommendations how to get them back in operational order? I have a bench top lab power supply. Was thinking of applying 15 volts at 1-2 amps for an hour and seeing if that kicks it back into gear. But want to check first if that's a good way of doing it or if I'm missing something else....