What if the lithium battery fails to charge after over discharging?

What if the lithium battery fails to charge after excessive discharge? I buy only half a year of SONY Ericsson MP3, the MP3 lithium battery has been used normally. Because I was busy with my work, I left it idle for about a month. Before, I forgot to turn off the switch on the machine. When I used it again to listen to music, it showed that the power was insufficient and then turned off. So I charged it, but I didn't charge it for a day. Because the market that sells this machine already classics changes course, guarantee is impossible, repair by oneself then.

First turn on the machine, take out the internal battery, test the most normal voltage, that the battery is not damaged. Analysis of the reasons may be due to the lithium battery charger has a charging control link, the excessive discharge of lithium battery cannot be charged. So I tried to add 5V direct current directly to both ends of the outlet line of the battery for forced charging. At the beginning, the charging current was very high (reaching over 400mA), and then gradually decreased and stabilized over time. After charging for 6 hours, put the battery back to the wiring of the original machine and start up and play normally. After a few days, when the power is insufficient, the original charger can be used to charge normally again.