# How do I boost charge a dead 3.7 V Li-ion battery?

I have a dead Li-ion battery from a WiFi device. Since I didn't use it for a couple of months, it's dead now.

I have read somewhere that boost charging is used to charge and bring the battery back to its original capacity. How much voltage and current should I supply to bring it back to life?

• If you have to ask this question, you may be a bit over your head. Improper handling and charging of Li-ion cells can be quite dangerous. Commented Oct 31, 2017 at 15:31
• What is the size of this battery? The answer depends on this. If the actual capacity is not known, tell the physical dimensions of the battery. Commented Oct 31, 2017 at 17:56

You can't "boost charge" a Li-Ion battery. When you say it is "dead", I assume it doesn't deliver any voltage/current. There could be two scenarios of what has happened.

1. The battery has a built-in protection circuit. When the (internal) cell voltage drops below certain threshold (like 2.5-2.9V), the circutrty disables the battery output.

2. The cell gets drained to actual zero due to self-dicharge parasitics. Then it is formally "dead".

There is a third scenario when the cell went dead after a catastrophic overdischarge (short), which destroyed internal conductors. I assume this is not the case here.

In first two cases there is a chance for recovery. You should apply a very modest "precharge" current (say, 100 mA). If the cell is just overdischarged and is shut down due to protection, it will quickly gain some voltage above the cut-off thershold, and the protection circuit will disengage. Then you charge the battery using normal means of your device.

If the cell has no protection and is dead by electrochemical depletion, there is still a chance that it will come back to life. However, studies show that the process of recovery is unpredictable, and in no case the cell can be restored to its original capacity. The result can be anywhere. See also some relevant discussion here.

A few years have passed since the last answer, so here's one in 2022:

You can revive a cell that is below 2.5/3.0V (whatever its datasheet specifies as the V_min) provided that

• the cell has not fallen below 1.5V for longer than a week,
• the cell reaches V_set (see below) within 1-3 minutes,
• you understand that while most cells won't explode after this procedure, some may, so do not take previous positive experiences for the sign that this will always work. In short, you need to watch the cells the first several cycles. Some heat is ok (60°C), but burning hot is not.

How to revive the battery:

1. Set max current to 0.1C (if you need an explanation on this, I kindly ask you not to burn your house and to discard the cell)
2. Set voltage to anywhere over V_min, e.g. 3.1V
3. If you reach the voltage within minutes, continue charging according to the datasheet, usually 0.5C is completely safe.

Enjoy! But…

Discard the cell if…

• if the cell does not reach V_set within 1-3 minutes (depends on type - simply if you can see that the voltage is not rising, give up)
• if the cell charges properly, but then drops voltage within one day, give up.
• if the cell bulges, produces gas.

Do not take warnings lightly. I am not covering my backside, but rather speak from the perspective of burned fingers and furniture.

Try do a couple of charge / discharge cycles. First charge up to 4.1 V then use a power led or a power resistor like 10 ohms for discharge until the battery reaches 1.2 volts. Then do the same thing more 2 times. Usually, it works for me.