How do you solve the problem that lithium battery cannot charge after over discharge?

What should I do if the lithium battery is not fully charged after being over-discharged? I buy only half of a Sony Ericsson MP3, the MP3 lithium battery such as the use has been normal. Because I was busy with work, I left it for about a month. I forgot to turn the switch on the machine to the off position. When I listened to music again, it showed that the battery was low and then turned off. Then it is charged, and it can be charged for one day. Since the store that sold this machine has already changed course, the warranty is impossible, so I will repair it myself.

First turn the machine on, take out the internal battery, and measure the voltage is normal, indicating that the battery is not damaged. Causes may be due to the lithium battery charger charging control link, over-discharge of the lithium into the electric charge. Then try to charge 5V DC directly to the terminals of the battery forcibly charging. At the beginning, the charging current is very large (up to 400mA), and then the current gradually decreases and stabilizes with time. After charging for 6 hours, put the battery back to the wiring of the original machine, and boot everything is normal. After a few days, when the power is insufficient, the original charger can be charged normally.