Evaluating Sanyo 18650 Cell Capacity, Tablet Battery Replacement & TP4056 Charging System

Hello, I'll start with the fact that I have several Sanyo 18650 cells that an old laptop battery. I have a few questions
1. I want to check the capacity of these cells, what difference will be when checking the capacity of the method: a) charging the battery and discharging it with a resistor e.g. 10 ohm to 2.5 V and checking the time, measuring the voltage with a multimeter b) using it to discharge the active cells load (I do not have one).
I don't need to buy or make a circuit if the difference would be up to 100mAh.
2. The 3.7V tablet battery has gone down and I would like to replace it with 18650, do I need to apply excessive discharge protection like this before the battery? http://www.allegro.pl/ShowItem2.php?item=6650383072
3. I would like to charge the batteries and use the mouse, if I connect the Tp4056 charging system to the battery, will I be able to charge (maintain) the batteries and use the tablet?
4. Does the use of the security from the link above make any sense if I would like to place the link in a 3xAAA bicycle flashlight?
I apologize for any language errors, post written by phone.

adamos11 wrote:

Does the use of the security from the link above make any sense if I would like to place the link in a 3xAAA bicycle flashlight?

No. Before excessive discharge occurs, the flashlight will stop lighting.

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1. I want to check the capacity of these cells, what difference will be when checking the capacity of the method: a) charging the battery and discharging it with a resistor e.g. 10 ohm to 2.5 V and checking the time, measuring the voltage with a multimeter b) using it to discharge the active cells load (I do not have one).
I don't need to buy or make a circuit if the difference would be up to 100mAh.

The current will change during discharge, but you can eliminate the resulting errors by measuring the voltage e.g. every half hour, in a short period of time the change in voltage (and current) will be small, so you can accurately count and then add up for all compartments.

Many modern meters have the ability to send data to a PC, later the data can be thrown into a spreadsheet, in addition to accurate capacity calculation, you can make characteristics of how voltage depends on the remaining charge.

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2. The 3.7V tablet battery has gone down and I would like to replace it with 18650, do I need to apply excessive discharge protection like this before the battery? http://www.allegro.pl/ShowItem2.php?item=6650383072

If the factory battery had (for the most part it is) it is better to give.

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3. I would like to charge the batteries and use the mouse, if I connect the Tp4056 charging system to the battery, will I be able to charge (maintain) the batteries and use the tablet?

This will affect the charging process if the TP4056 is additionally charged with the tablet's current then it will not recharge or stop charging, the second case will end with premature battery wear.

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4. Does the use of the security from the link above make any sense if I would like to place the link in a 3xAAA bicycle flashlight?

On a bike, when dusk falls and the light shines dimmer, it is easy not to notice when it is the right moment that it should be turned off to prevent excessive discharge.
Is this flashlight bulb or LED?

There is a diode in the flashlight, a flashlight like this https://www.24sklep.pl/6572-thickbox_default/latarka-diodro-led-3w-cree-p3830-zoom.jpg

When it comes to calculating the capacity, I connect the multimeter in series and check the current in A, if it drops by 1 A per hour from 4.2V to 3V (here a multimeter in parallel), the capacity in the battery is 1000mAh? I count correctly or understand something wrong?

adamos11 wrote:

There is a diode in the flashlight, a flashlight like this https://www.24sklep.pl/6572-thickbox default / flashlight-diodowa-led-3w-cree-p3830-zoom.jpg

It will actually stop shining before the battery is over-discharged. If the flashlight is fairly well made (which I doubt) it can be modified, see the forum www.swiatelka.pl there are specialists for such modifications.

adamos11 wrote:

When it comes to calculating the capacity, I connect the multimeter in series and check the current in A

You can measure current or voltage because if the resistance is constant it can be easily converted. You still need to control the voltage so that it does not overcharge.

adamos11 wrote:

... if it drops by 1 A per hour from 4.2V to 3V (here a multimeter in parallel) is the capacity in the battery 1000mAh? I count correctly or understand something wrong?

You don't measure and record voltage, then you count the current and charge.
For example, if you have a 10? resistor, at the beginning 0.42A will flow because the voltage is 4.2V at such a current for 0.5h will deplete 0.21Ah of charge.
At the end of the discharge process the voltage will be 3V so 0.3A will flow and only 0.15Ah of charge will drain for half an hour. The time interval between measurements should be such that the change in voltage is small. Finally, you add up how much load you have unloaded in each time interval.