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I have an LG G3 phone that I want to use as a stationary device and leave it hooked up permanently. I prefer not to do it with a battery for various understandable reasons.

My questions are:

What parts do I need to convert USB 5V to 3.8V? (I guess a voltage regulator, but is that all I need? and which one to get?)

What other factors (such as current) should be considered and how to deal with them?

Daniel
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NoamC
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    `I prefer not to do it with a battery for various understandable reasons.` Such as? – Passerby Jun 08 '17 at 23:36
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    I don't understand why you'd want to use a phone (cell phone?) without a battery if it is intended to be used with a battery. – Peter Bennett Jun 08 '17 at 23:38
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    most of the 20+ phones i've powered this way won't turn on unless you put a small resistor across one or more of the "middle" (non V+/G) contact of the battery. Ohms and pinout vary, so google it, but generally a 1k from V+ to the middle assures the phone there's a battery. you also need a supply rated higher than the mere charger, since you wont have the battery to absorb spikes. 2A min. – dandavis Jun 09 '17 at 07:51
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    @Passerby: batteries need replaced. would you want to buy a $35 battery for a phone that's worth $10? many phones wont boot with a dead dead battery, but they can be useful still – dandavis Jun 09 '17 at 07:53
  • The simplest of course is leave the battery on and plug it into a charger, yes eventually the battery will wear out. What if you plug it in to a charger without the battery in place, does it power the phone? As answered below, yes in theory you can simply apply the right power to the terminals, so long as you do it in a safe manner. That is all the battery is doing. – old_timer Jun 09 '17 at 19:08
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    I think it is a very reasonable need being able to use just with a cable and even without a battery plugged. The use cases are very similar to Laptops but i would say that all laptops work with cable and battery unplugged. – Daniel Perez Jun 22 '22 at 21:28
  • Did you try to remove the battery and power the phone with the cable only? I bet it will happily boot. You will need a somewhat stiff wall adapter depending on the use you want to make of this phone. – Vladimir Cravero May 31 '23 at 20:43
  • @DanielPerez "all laptops work with cable and battery unplugged" unfortunately, no. I had an old laptop (either HP or Lenovo, don't recall) which did not work from PS alone. Laptops and phones can be integrated in many DIY projects, which makes this question very interesting. I am just not sure there is a generic answer due to battery interfaces often being application-specific. – Maple May 31 '23 at 21:32

4 Answers4

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There should be no big problem to replace internal battery with external DC source. In my former place of work the software people routinely (and without any reservations!) used various benchtop variable PSU to feed phones and tablets under development directly to battery connector, because the internal charger management firmware/software was broken at the time.

From your level, the module like "Mini LM2596s 3A DC to DC Buck Converter Power Supply Step Down Module" will do the job. You can set the output voltage to something in the range between 3.6 to 4.2 V, although the phone might still be confused regarding "battery charge status". If the confusion won't be gone after several power-on-off cycles, then you are out of luck, since phones use pretty sophisticated methods to check battery health status.

Also, if the battery has a built-in thermal sensor (usually as a third contact on battery case) , you might need to simulate "good thermal status" by connecting a 10k resistor to ground. Your battery (BL-53YH) does have two additional contacts, but in recent phones they are used for stick-on near-field antenna, so no worry about them.

However, it might have more economical sense to get a cheap replacement battery from e-Bay or AliExpress, they seem to be in $10 range in qty.1. At least the risk will be much less than from developing a regulator in battery fromfactor on your own, with AC-DC wall supply (or carrying a USB cable), or other ugly stuff.

Ale..chenski
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  • I recently bought that step down module to use in a motog 5 cedric. Even using the built-in thermal sensor removed from the battery it can't boot. Keeps rebooting. – imbr Apr 29 '21 at 11:48
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In theory, I don't see why applying the specified battery voltage on the correct battery terminals would not work. Try to avoid overvoltages!

Obvious reasons are not obvious to everybody. I assume you don't want the battery in the loop so you don't have to worry about it aging over time, bloating and potentially causing problems?

A linear voltage regulator would probably do the trick. I would personally add a good amount of capacitance between the regulator and the phone to smooth out any sudden changes in your phone's power consumption. If you want to ensure you never go over a safe voltage, a Zener diode would be your friend.

Good luck, and let us know of the outcome!

MAB
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I have just put 5 volts right on the + and - of were the battery would go. They do have another pin I guess for sense.

I did it on 2 old cellphones that the battery went bad on. But they only stay going for about a day. It thinks the battery is draining down very low so it turns off. I guess have to put something on the 3rd pin but I don't know what.

I just solder the wires on the pins and made a hole in the back cover to put the wire though were the battery would go.

Did a little video on YouTube of it.

-Raymond Day

Raymond Day
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Why don't you just plug the USB into your phone ? And if you want to convert 5V to 3.8V you have multiple possibilities. You could use a LM2576 or directly divide the voltage with resistors.

Orgoss
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