Hello!
I try to power the T24P123 5V display module from a 3.7V Lithium cell phone battery BP-6M (I have 2 pieces of these chinese clone, not Nokia original).
The T24P123 datasheet states that the module can be powered from 3.7 to 5V (I have the 5V flavor, not the 12V one), power consumption 0.6W. As long as BP-6M has at least 4V the display works. At 3.9V T24P123 does not turn on. The trouble is that BP-6M slowly discharge by doing nothing to about 3.86V, and when I need the display it's not turning on.
To extend the battery's usage I added a HW-553 DC-DC step up module 0.9V - 4.5V input, 5V output. Now the display turns on even at 3.8V.
My question is: will the DC-DC step up converter drain the battery until it reaches 0.9V (the lowest voltage the converter can use)? If so, the battery will be damaged if discharged below 3.2V. Is the included protection board from the cell phone battery enough to cut off the power before damaging the battery from overdischarge?
Do I need a different DC-DC step up converter with a minimal voltage of 2.5V? Like this https://www.aliexpress.com/item/1005003187753835.html ? The output can be set at 5V, and input is from 2.5V.
Yes, unless the battery has some protection. It will be damaged around 2.5V, but is better to stop draining it at about 3.2V.
You could use some voltage supervisor. But as you will need also to charge the battery you could take a look at some module like the TP4056, you can find it in aliexpress also. It has overcharge/discharge protection.
Only take into account not charging and using the device at the same time, or add some additional protection as explained in several tutorials for that module.
I have a dedicated charger for the phone batteries, so no need for charging inside the device. I simply swap the batteries.
The is very little space inside the housing (not shown in the pictures). It's better to use a DC-DC step up to 5V with overdischarge protection. Couldn't find any with a minimal input voltage more than 2.5V.
I also found this BMS https://www.aliexpress.com/item/32981217292.html , but the overdischarge voltage is 2.75V .
I also dismantled a Samsung EB535163LU Lithium battery, and inside it's a PCB (BMS). I suppose BP-6M has also one, because of the gold plated contacts.
Ok. Maybe it has already protection, or it relays in the external charger, I don't know.
Otherwise you could get these BMS in aliexpress also:
Search for battery overdischarge protection, or something like that. It's dirty cheap.
Other option would be to do it yourself with the voltage that you want. With a voltage supervisor and a mosfet.
I've discharged the Li battery through the step-up module. The battery went dead at about 2.95V, and charged just fine to 4.17V after that.
Conclusion: the cell phone batteries have overdischarge protection, the particular BP-6M to 2.95V.
All cell phone batteries have built-in overcharge, overdischarge and short circuit protection. If you disassemble the battery you will see PCB under the plastic with the terminals. For 18650 batteries that have an overheat protector. For them, you need to mount the PCB shown by gromit1.
