# Help a Beginner... Charging a Lithium Battery With a DC Power Supply?

Discussion in 'General Electronics Chat' started by David Lin, Jun 12, 2016.

1. ### David Lin Thread Starter New Member

Oct 11, 2015
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Hello. I have a 3V, 1.3mAh li battery that I am attempting to charge. I initially placed a voltmeter across the battery and it read approximately 2.4V.

I attempted to charge it to its nominal voltage of 3V with a DC power supply (I know people don't recommend this, but I'm really just doing this to play around and am not leaving the battery unattended.) Supply was hooked in series with a resistor to the battery. Articles recommend a max charging current of approximately 0.7C, so I chose a max charging current of 1mA. I chose a charging voltage of 3.1V. So if I set my supply to 3.5V, I chose a resistor of (3.5-3.1)V / 1mA = 400ohms.

However, when I tried this, the battery barely drew any current, as read on an ammeter, and for the most part, the battery voltage stayed at 2.4V (I would occasionally turn off the supply to read the voltmeter I hooked up across the battery). I think it had about about an hour and a half before I totally unhooked the circuit.

What did I do wrong?

2. ### Lestraveled Well-Known Member

May 19, 2014
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First off, are you certain that the battery is 1.3mAh. That is .0013 amp hours. What is the part number of this battery? Perhaps it is really a 1.3 AH or 1300mAh battery.

A 2032 coin cell is around 200mAh (.200 AH)

Last edited: Jun 12, 2016
3. ### David Lin Thread Starter New Member

Oct 11, 2015
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Yeah I'm very certain haha, it's a super small battery. I forgot the number, but it's from paansonic.

4. ### Techno Tronix Member

Jan 10, 2015
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Check the full charge voltage, which is commonly 4.20V/cell, and set the threshold accordingly. Make certain that none of the cells connected in series exceeds this voltage.

5. ### Lestraveled Well-Known Member

May 19, 2014
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1,239
Is your battery 1/100 the size of this one? Do you need a magnifying glass to pick it up? Will it fit inside of the "O" at the top of the quarter. If the answer is no then, I don't think you have the amp hour rating right.

6. ### BobTPH Senior Member

Jun 5, 2013
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3V lithium batteries are typically primary cells and not rechargeable.

Bob

7. ### Lestraveled Well-Known Member

May 19, 2014
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You haven't noticed all the cordless power tools going to rechargeable lithium batteries? Pretty much all the batteries in new laptops are lithium. Yes, some of the lithium batteries are not rechargeable, but there certainly is a large selection of rechargeable lithium batteries.

8. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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The CMOS memory backup batteries you are talking about are charged with a MAXIMUM of 1 mA. Constant voltage charging of 3.3 to 3.5 volts. MAXIMUM discharge current for batteries under 2mAh is 10 micro amps. (.01 milliamp).

Why are you messing with that scrap? 500 cycles or 3 years and they are 80% spent or dead already.

A new box of 100 is \$159. Panasonic VL-621

9. ### Lestraveled Well-Known Member

May 19, 2014
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I learn something new every day.

cmartinez likes this.
10. ### ian field AAC Fanatic!

Oct 27, 2012
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1,197
If you're a beginner charging lithium cells - get some good domestic fire insurance.............................

The full charge terminal voltage is absolutely critical and varies a little with the various sub chemistries.

You need to limit the charging current to a safe value, never exceed the rated terminal voltage and don't leave it float charging.

Oh - and make sure its intended to be recharged - some lithium cells aren't.

11. ### BobTPH Senior Member

Jun 5, 2013
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Yes, and those batteries are 3.7V, not 3V. The 3V batteries, like CR2032 are non-rechargeable.

Bob

12. ### ian field AAC Fanatic!

Oct 27, 2012
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Around 3.6 - 3.7V is the standard nominal voltage for most lithium cells. There are some at 3.0V though.

The full charge terminal voltage for rechargeable types is generally around 4.2V - but varies with exact chemistry - some early types could flame if you charge them above 4.1V. 4.2V is currently the most common, but I've seen a datasheet for a type that requires 4.3V.