Self charging and not charging to full capacity

My Sumsung Galaxy S3 Mini GT-I8190 started charging by itself. The battery can be almost fully charged and nowhere near a charger and I will hear the charging tone and see the little charging icon (lightning flash) on the battery icon, like when I place my phone on charge. This happens at irregular intervals numerous times during the day. I've replaced the battery and I've even done a system reset but it still happens and when I charge it (either with a normal wall charger or my USB charger) it restarts when the battery is at about 80% and keeps restarting, charging, restarting, charging and then eventually goes blank. Except for this my phone seems to be working fine. Is there a software solution?