Electronics > Repair
Charging Lithium Battery
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2X:
Hello,
I want to charge this battery with a universal charger. The original charger is missing and I can't find a used one. Can I charge this battery with a universal charger? I open the battery and inside there is a PCB (I beleive this PCB is for short circuit protection of the battery?)

I don't know what is the purpose of the "D" and "C" pins; I made a schematic and these pins are connected to U1 (I didn't find any datasheet of this chip).

The "TH" pin I is for thermal protection?

Any advise?
indeterminate:
No you cannot use a universal charger.
Many fires are started by people using the wrong charger on Lithium batteries.
The PCB is for battery protection and possibly cell balancing it will disconnect the battery in the event of under / over voltage
you should be able to find a charger for a 7.4v 1500mah battery but there is no guarantee that it will work or be safe.
the IC on the battery PCB may need to communicate to the charger
2X:

--- Quote from: indeterminate on December 12, 2024, 10:19:23 pm ---No you cannot use a universal charger.
Many fires are started by people using the wrong charger on Lithium batteries.
The PCB is for battery protection and possibly cell balancing it will disconnect the battery in the event of under / over voltage
you should be able to find a charger for a 7.4v 1500mah battery but there is no guarantee that it will work or be safe.
the IC on the battery PCB may need to communicate to the charger

--- End quote ---

I found the below. Do you beleive it will be ok? It refers that it has "USB IN: Adaptive Input Current Limitation, Over Heat/Reverse Connection Protection"
Manufacturer Product Number: DFR0564
https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/720/DFR0564_Web.pdf

From the manual above:
Warning
Users can choose to use DFRobot 7.4V lithium battery, or buy a 2s 7.4V lithium battery with battery protection
circuit. Lithium battery manufacturers usually pack two identical 3.7V lithium batteries (usually lithium polymer
batteries or 18650 lithium batteries) in series and a battery protection circuit. This module is unbalance
charging type. When the battery connector is a JST-XH2.54 3P, please use a dedicated balance charger. This
module fits to the batteries, which only have a 2P connector (such as JST-HX2.54 2P or DC2.1mm power jack). It
is not recommended to use 7.4V lithium batteries without battery protection circuits.
Do not charge any two 3.7V lithium batteries in series by yourself. Otherwise, the batteries are probably
overcharged, causing it to be scrapped or even explode.

Thanks for your useful reply.

garrettm:
I would NOT use a "universal" charger for any lithium battery. The exact chemistry type of the cell changes the set point voltages and can't be known by the charger. Additives like cobalt can change the max cell voltage. So I'd look at the pouch label and see what it says. In your case, 4.35V per cell.

If any lithium cell is below 2.5V just throw it away. Irreversible chemical reactions happen below 2.5V that damage the cell. If above this voltage, then the cell is likely recoverable.

7.4V ==> 2x 3.7V cells. This is likely the average voltage of the discharge curve.

I would not charge these cells in series.

You can charge each cell individually using a variable DC power supply and monitor the current till it reaches the cut-off threshold.

Below are some notes I have for my own Li-polymer cells. But generally, the information here is valid for most Li-Ion / Li-polymer cells, with the exception of LiFePo that have an entirely different charge algorithm.


--- Code: ---Lithium Polymer (Lipo) / Lithium Ion (Li-ion)

Standard Lipo Charge Algorithm:
If V_cell <= 2.50 V, discard: cell is likely damaged / recovery is unlikely
If 2.50 V < V_cell < 3.00 V, CC charge at 0.05 to 0.10 C (3.00 V compliance limit)
If V_cell >= 3.00 V, CC charge at 0.20 to 1.00 C (4.20 V compliance limit)
Once V_cell = 4.20 V, CV charge until current < 0.10 C

Long-life Lipo Charge Algorithm (~4x cycle life):
If V_cell < 2.50 V, discard: cell is likely damaged / recovery is unlikely
If 2.50 V <= V_cell < 3.35 V, CC charge at 0.05 to 0.10 C (3.40 V compliance limit)
If V_cell >= 3.35 V, CC charge at 0.20 to 1.00 C  (4.00 V compliance limit)
Once V_cell = 4.00 V, CV charge until current < 0.10 C

Ultra Long-life Lipo Charge Algorithm (~12x cycle life):
If V_cell < 2.50 V, discard: cell is likely damaged / recovery is unlikely
If 2.50 V <= V_cell < 3.35 V, CC charge at 0.05 to 0.10 C (3.40 V compliance limit)
If V_cell >= 3.35 V, CC charge at 0.20 to 1.00 C  (3.85 V compliance limit)
Once V_cell = 3.85 V, CV charge until current < 0.10 C

Precharge | CC 0.05-0.10C, 3.0V compliance | 2.5V < Vcell <  3V
Bulk      | CC 0.20-0.70C, 4.2V compliance |        Vcell >= 3V
Top Off   | CV 4.2V                        |        Icell >  0.10C
Terminate | disconnect from charger        |        Icell <= 0.10C

  CHARGE (voltages WRT charger, not cell)

No energy is stored in a Lipo cell when charged below 3.40 V.
Roughly, charging at 3.40 V (min) provides 0-1% SoC and 4.20 (max) 100% SoC.
Charging a cell when 2.50 V < V_cell < 3.40 volts is pre-charging.
Bulk charging occurs when 3.40 V <= V_cell < 4.10 V (0 to 90%)

3.4   1%
3.5   3%
3.6   5%
3.7   9%
3.8  36%
3.9  62%
4.0  73%
4.1  89%
4.2 100%

  STORAGE (votages WRT cell)

Li-ion cells should be stored in a partially discharged state: keep cell voltage
between 3.8 (max) to 3.4 (min) volts for long term storage. This corresponds to
roughly 40% to 0% state of charge.
 
If cell voltage drops below 2.5 volts, permanent damage will occur.

  DISCHARGE (votages WRT cell)
 
Never discharge Li-ion cells below 2.5 V, as this can cause permanent damage to
the cell.
 
Terminate discharge at >= 3.0 V for faster recharging.
--- End code ---
garrettm:
I'd unsolder the cells from the PCB before recharging them and once tested to be working okay, resolder them back and charge normally in the equipment it was made for.

You may end up needing to buy new pouch cells to replace these if one of the cells is bad or has low capacity WRT to the other cell.
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