We are not fixing audio today. I upgrade my old friend Dewault 920 . This hard working guy was in service with me from 2010 . Got good reputation and perfect resume . As you know this tool works for electrical jobs and small projects and use not powerfull NI-MH battery 7,2 Volt. After 5- 9 month of work you have to buy new battery. In this case we will transfer it to lithium 7.4 volt battery . We use two 18650 lithium elements in series. Gentle soldering requaired. Create new charge port and drop new batteries in old plastic shell . DO NOT USE OLD CHARGER !!!! It will damage new Lithium battery.
In my case i used simple audio RCA plug as charging port. Charger we will use 8.4 volt 1-2 Amp for lithium batteries only. 8.4 volt only with protection and current control . Will do update how my upgrade process goes.