How can I charge removed iPhone 4 battery externally?
How can I charge iPhone 4 battery externally easily to boot up my phone? I have a dc adapter that I can adjust it to 4V.
You could try and momentarily attach a 9V battery to the + and - battery contact. +to+ -to- this will wake up your battery, but it will not charge it. Problems with an external charger is that you are missing the feedback circuit to prevent the battery from overcharging etc. There are some reversed engineered circuits as well as charging circuits, but all those are new construction.