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I have a project in mind, where I need alot of parts that quickly would make this project really expensive.
Then I thought that, all the parts I need is already in a smartphone, but I don't need a battery.

Is there a easy way to replace the battery and just connect it to some off the shelf power supply/board ?
(I am thinking the phone always draw the same power, but I am not sure if that is the case)

[edited]
I wanted to make smart-home-panels, where I could watch youtube and use them for other things too.
I would need a screen (must likely touch screen), some computer board (looking at a raspberry pi zero with Kodi, since it is slow on "Raspberry Pi OS with desktop" in display mode otherwise), there is also a need for Wifi and a speaker (maybe also a camera).
The parts would add up fast, but if I buy a used smartphones for a lower price, most of all the parts are there already.
The battery would be the only part that could be a problem (outside of no-updates to the old android OS, but maybe I will just look at those phones, that are used alot on homebrew sites)

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  • \$\begingroup\$ I modified an old smartphone (Oppo Find 5) to work directly from a USB power supply by connecting the battery contacts to 5 V directly or via a diode to lower the voltage slightly. That works for that model phone. There is no guarantee that this will work for other phones as well! In the end, you will just have to try what works. Some phones need a lot of current during startup and an external supply might not be able to deliver that amount of current or the circuit inside the phone prevents such a high current from flowing. Then the phone will keep rebooting. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 1, 2021 at 9:37
  • \$\begingroup\$ If you don't need the battery, why can't it still be in the phone, why it must be removed? \$\endgroup\$
    – Justme
    Commented Nov 1, 2021 at 10:05
  • \$\begingroup\$ I don't need to take out the battery, but I feel that none-stop powering over the power port could be a problem. electronics.stackexchange.com/questions/325480/… \$\endgroup\$
    – Repeller
    Commented Nov 1, 2021 at 10:53
  • \$\begingroup\$ Today's smartphones are smart enough to protect the battery from overcharging and related problems, unless there's a problem reading the battery temperature. So, why don't you consider keeping the phone plugged to its original wall charger permanently? Removing the battery and tricking the circuit is a more complicated and unguaranteed work. \$\endgroup\$
    – Rohat Kılıç
    Commented Nov 1, 2021 at 11:30
  • \$\begingroup\$ Most of them will not accept it. There might be exceptions. \$\endgroup\$
    – winny
    Commented Nov 1, 2021 at 12:48

2 Answers 2

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If you want to power a cellphone from a power supply you will likely need the value of the thermistor that is used in battery pack for this phone. You probably see 3 or 4 connection points where the battery goes. One of those is for monitoring the battery temperature.

If you are lucky, it is just a thermistor and connecting same value resistor from the pin to ground will make the phone happy. If you are unlucky, then the thermal monitoring pin is an actual data line that sends information about the temperature, in which case it gets extremely difficult to hack it.

Also, take into account that the components in your phone have pretty obscure connectors and rarely have pinouts provided. So if the plan is to take the phone components apart and reuse them in another project, you can pretty much drop that idea right now.

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  • \$\begingroup\$ I suspect connecting just thermistor will not be enough if power is supplied through charging port. Most likely power supply will have to be hacked as well to connect directly to battery inputs. \$\endgroup\$
    – Maple
    Commented Nov 1, 2021 at 9:26
  • \$\begingroup\$ The battery monitoring system (BMS) will very likely be on the phone’s motherboard, so a power supply would have to emulate a battery very convincingly for such a setup to work. In what scenario would you get hold of a phone with no battery significantly more cheaply than a phone with a battery? \$\endgroup\$
    – Frog
    Commented Nov 1, 2021 at 9:27
  • \$\begingroup\$ I wanted to make smart-home-panels, where I could watch youtube and use them for other things too. I would need a touch screen, some computer board, there is also a need for Wifi and a speaker (maybe also a camera). The parts would add up fast, but if I buy a used smartphones for a lower price, most of all the parts are there already. \$\endgroup\$
    – Repeller
    Commented Nov 1, 2021 at 9:40
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    \$\begingroup\$ @Frog An older model with no replacement perhaps, I don't know. \$\endgroup\$
    – Willy Wonka
    Commented Nov 1, 2021 at 15:54
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If you connect a DC supply to the battery terminals it will probably work just fine,.

I did this once with a Motorola Micro-TAC that I found on the road. (someone left it on the roof of their car)

I powered it with alligator clip leads and a lantern battery. In this way I could be contacted by the owner, and was able to return the phone and the remains of the busted battery pack.

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