The second string made it an unwanted double at Longmead when they joined the senior team by losing in Kent.
Ade Azeez gave the Addicks an early lead before Purcell lobbed John Sullivan after 32 minutes to square things up.
Lively striker, Frannie Collin, settled the game shortly after the interval with a stunning free-kick.
Charlton: Sullivan, Muggeridge, Osborne, Ajayi (Saraiva 46), Fox; Jordan, Bover (Poyet 60), Hayes; Pigott (Sho-Silva 60), Clarke, Azeez.
Subs not used: Phillips, O’Hanlon, Holmes-Dennis.
Goal: Azeez 6.
Tonbridge Angels: Worgan; Judge, Walder, Browning, Kember; Schulz, Davis, Piper, Purcell; Collin, Koranteng.
Subs: King, Scarborough, Crimmen, Leighton, O’Brien, Collins.
Goals: Purcell 32, Collin 47.
Referee: Mike Bull (Essex).
Attendance: 723.