Powering on phone with dead battery

[Digitalio]

My phone's battery has died recently, so it doesn't charge at all and the charging LED just stays blinking forever and the phone doesn't turn on. I wonder if it's very difficult to start the phone without the battery at all, simply from a 3.6V power supply?

[anvoice]

Can you open the phone easily to get to the battery and circuitry? If so, get the battery out and try to find the exact voltage it nominally provides (might be 3.8V for example), and you can try providing that exact voltage to the correct terminals on the phone.

I've also had luck opening an old tablet, taking out the battery, and charging it directly by applying a voltage to it (don't try unless you can limit the current going in, i.e. you have constant current capability on your power supply). It worked long enough for me to to turn on the tablet.

Third, if you want to continue using the phone with any degree of convenience (and assuming again a removable battery) you could buy a spare and use that.

If you can't open the phone to get to the battery, you're likely out of luck.

[Daixiwen]

If you manage to open the phone, the cell is completely flat (under 2.5V) and you want to try and recharge it with a power supply, be sure to use a very low current, until the cell voltage reaches at least 3.0V. Using too a high current on a flat cell can damage it and transform it into a fire hazard.

[Renate]

If the battery is really dead, you don't want to replace it and you want to run the device tethered to power, you can.
Many (most? all?) cell phone batteries have extra connection for thermistor and/or analog/digital identification circuits.
If you want to destroy your battery pack, cut the actual cell foil connections and recycle the cells and hook up 4V.
This way you can retain all the other circuitry in the battery pack.
(This is also a good way to monitor sleep/processing/CPU throttling.)
OTOH, I'm sure ebay has the replacement for cheap.