what did I ruin in my '95 jeep by jump starting it?

I left an interior light on, I jumped my '95 jeep cherokee sport with a 50 amp quick start charger. It ruined something. It won't take a charge. when I try charging it with a normal charger the hazard lights start blinking. the ignition won't even attempt to turn over. The battery is perfectly fine. what is this and how major will it be to fix