# Charging Li-ion batteries in series

Recently, I bought a DC 12300, a 12V battery with high capacity 3000mAh and I got a charger 12.6V and 500mA output. First thing I did when I got the battery, I measured its voltage and it was 2V. After 6 hours of charging, (I presumed that it was 3000mAh-6 hours of charging). I got the same result. But as batteries are all connected in series their capacity is still 1380mAh.

My first question is: Did I overcharge the battery considering the fact that I charged 1380mAh instead of 3000mAh? It says also "Over-charge/discharge protection".

I proceeded by measuring the voltage individually for each small battery and I got 3.7V and 0V for 2 others.

My second question is: Can I try to recharge the battery separately using a 4V charger or my battery is definitely damaged?

• The charged one is it connected to charger's (+) or (-) ? Commented Jan 7, 2015 at 4:27
• A lithium ion cell measuring zero volts is not recoverable by charging - send it back. Commented Jan 7, 2015 at 4:30
• The battery was dead (broken) already when you bought it. It's not going to get better by trying to charge it. I Agree with Chris, send it back.
– PkP
Commented Jan 7, 2015 at 5:03
• "The charged one is it connected to charger's (+) or (-) ?" I don't really know. Thank's a lot for your comments. I will try to recover my money back. Commented Jan 7, 2015 at 22:30

Measuring the battery voltage "as received" prior to charging "is always wise"

However, this is a scam.

Battery

• Voltages add if cells are in series

• mAh capacity stays the same if cells are in series

The battery contains 3 x 3.7V cells (nominal) rated at 1380 mAh each.
Placing 3 in series would at best give you a 11.1V x 1380 mAh battery.
IF they had been in paralle it would nominally be a 3.7V x 4140 mAh battery
So the 12V x 3000 mAh claim is spurious.

A LiPo cell has a
maximum voltage of 4.2 V (So 3 x 4.2 = 12.6 = Vmax_charged)
an average voltage over the whole discharge of ABOUT 3.6V or 3.7V / cell
and a minimum voltage of about 3V/cell.

Discharge tyo much below 3V/cell is liable to damage the cells and discharge to 2V/cell will fatally damage the cells.

So not only did they sell you fake junk, they sold you dead fake junk :-(.

There are many of these for sale on the internet at various prices.

IF you bought one from Seeed studios or Deal Extreme you could very likely get your $back. From elsewhere YMMV. Dead Jim You Tube. DX.com - capacity claim 1500 mAh V still suspect <- Somewhat reputable seller. Amazon$31.80 junk

Amazon $28 whatever Bang good$18.10 low price junk

Fasttech $16.45 even cheaper junk ## :-( ADDED 1/2016 in response to reader query. How is it fake? I have a couple of this exact same battery, and they work fine and they each report 12.6V when fully charged, from the 3 x 4.2V cells. That's how you measure voltage in series. Read the above explanation carefully and you should see where the claims are wrong. The 3 x 4.2 = 12.6V is indeed what he should see when fully charged - that's what you get, which is good. He gets ~= 2V which is fatally bad. Even if the 3 cells in a 3S pack were 500 mAh, or even 50 mAh capacity, they would still measure 12.65V when fully charged, so battery voltage within range tells you very little. Battery voltage outside range tells you much. Vbattery • over about 12.8V is very bad and • under about 9V is also bad. • under about 8.5V is possibly fatally bad (2 x 3V marginal and 1 x 2.5V death's door). • under about 7.5V is junk. When you place cells in series (3S here) the voltages add (as you say), but the mAh of the combination is that of the lowest capacity in the string - in this case 1,380 mAh for THE WHOLE string as they are all have the same capacity = 1380 mAh. LiIon and LiPo cells have a mean operating voltage of around 3.6V to 3.7V and this is whyat is usually used for quoting battery voltage. Vmax is 4.2V/cell and SOME manufacturers use this voltage when specifying battery voltage, but this is a marginal practice - anyone who does it without comment is quite likely to be "cutting corners" elsewhere. If you add batteries in parallel (3P if you did that here) (they must all be the same voltage) the mAh ratings DO add but Vout is V for one battery. So his battery could legitimately be described as [10.8V, 1380 mAh] (at 3.6V/cell), or [12V, 1380 mAh] (at the marketing hype 4.2V/cell) OR [3.6v TO 4.2v, 4140 mAh] but NOT [12V, 3000 mAh]. That is what makes it fake. IF the cells used are in fact 1380 mAh (and they may be lower)(ask me how I know*) then capacity = 1380/3000 = 46% of claimed. That's fake, alas :-(. IF your version has 1380 mAh cells the same applies. The battery cam be 12V, 3000 mAh with 3 cells ONLY if it contains at least 3 x 3000 mAh cells. If readers disagree with this or do not understand it please do comment or ask - the aim here is to learn. • I've spent 6+ months in China on over a dozen electronics manufacturing related visits in the last decade - which has taught me a lot about what you may expect worst case. China can and does make excellent products. But, also, extreme rubbish if uncaring profit focused and/or ill informed resellers let them get away with it. Unfortunately, many do. Almost no specification or claim is trustable if the reseller does not stand behind it and has not done enough "due diligence" to be certain that their supplier is reputable and reliable. A very large proportion of product from "no name" manufacturers or suppliers does not meet claims and/or specifications to some extent. • Nop. I got it on Ebay for 18$ US. Thank's a lot for support. Commented Jan 7, 2015 at 22:43
• @NickGrigoriev EBAY may have an applicable refund policy. Commented Jan 7, 2015 at 23:41
• How is it fake? I have a couple of this exact same battery, and they work fine and they each report 12.6V when fully charged, from the 3 x 4.2V cells. That's how you measure voltage in series... Commented Jan 6, 2016 at 17:46
• @Cerin Read my explanation carefully and you should see where the claims are wrong. The 3 x 4.2 = 12.6V is indeed what he should see when fully charged - that's what you get, which is good. He gets ~= 2V which is fatally bad. || BUT When you place cells in series the voltages add (as you say) but tyhe mAh of the combination is that of the lowest capacity in the string - in this case 1380 mAh for THE WHOLE string as they are all the same. || If you add batteries in parallel (they must all be the same voltage) the mAh ratings DO add but Vout is V for one battery. So his battery could .... Commented Jan 7, 2016 at 9:55
• .... legitimately be described as 12V, 1380 mAh but NOT 12V, 3000 mAh. That is what makes it fake. IF the cells are in fact 1380 mAh (and they may be lower)(ask me how I know) then capacity = 1380/3000 = 46% of claimed. That's fake, alas :-(). IF your version has 1380 mAh cells the same applies. The battery cam be 12V, 3000 mAh with 3 cells ONLY if it contains at least 3 x 3000 mAh cells. || If you disagree with this or do not understand it please do comment or ask again - the aim here is to learn. [[6+ months in China in the last decade has taught me a lot about what you may expect .... Commented Jan 7, 2016 at 9:59

If the cells are protected and one cell charges faster than the other it's protection will cut it off and current will not flow the other battery in series. That is the function of battery management circuits.

Lithium ion batteries are fully charged at 4.2V, and discharged at about 3 V. During the process of charging and discharging the voltage changes. This makes it easy to know how much it is charged. A voltage around 3.7V is about half discharged.

It is possible to charge the cells individually, but limit the current and don't exceed 4.2V, and monitor the battery temperature. Many lithium batteries have built in protection for overdischarge. If the voltage goes too low, the output switches off. If a battery is discharged too low, it is probably damaged. There is some information on YouTube, how to revive lithium batteries that went dormant. Lithium batteries pose fire hazard.

That battery pack shown is a li-po pack with three cells in series. I fly RC airplanes and li-po packs are used for our electric planes. Special chargers are used to charge and balance the cells while charging in a series pack.

A cell below 3.00-volts per cell is over discharged / bad and "I" would not try to charge it. In an RC airplane a special voltage regulator / speed controller is used to make sure the batteries never fall below 3.00-volts per cell. This is a method of properly taking care of an expensive battery.

"Recently, I bought a DC 12300, a 12V battery with high capacity 3000mAh and I got a charger 12.6V and 500mA output."
Get a GOOD charger. Good charger here. You will probably need a power supply to go with it (here).

"First thing I did when I got the battery, I measured its voltage and it was 2V."
Battery is toast.

After 6 hours of charging, (I presumed that it was 3000mAh-6 hours of charging). I got the same result. But as batteries are all connected in series their capacity is still 1380mAh.
How'd you get the capacity?

"My first question is: Did I overcharge the battery considering the fact that I charged 1380mAh instead of 3000mAh? It says also "Over-charge/discharge protection"."
Nah, battery was toast before you got it.

I proceeded by measuring the voltage individually for each small battery and I got 3.7V and 0V for 2 others.
Two cells are 100% bad. You can never go below 1.7V in a lithium ion cell. It permanently kills the cell. I would try to use the other cell, because damaged cells can be dangerous.

My second question is: Can I try to recharge the battery separately using a 4V charger or my battery is definitely damaged?
I wouldn't try to charge it. Using it alone is a safety hazard.

For batteries, check out Hobbyking.com. 3S lipoly batteries are similar to 12V (nominal 11.1V, max 12.6v). Make sure you get a GOOD charger too and follow safety guidelines for lipoly batteries.

That is correct

In series connection, Voltage only are added not the mah rating

While in parallel, Voltage stays the same but add all the mah rating

• I think you need to clarify what you're answering with "That is correct". As it stands, I can't see which aspect of the original question you're trying to cover with that sentence.
– pipe
Commented Feb 15, 2016 at 14:17
• Hello AVG1981, welcome to EE.SX! Please do try to answer all of Nick's original questions. Try the edit button below your answer. You will get much more reputation for a complete, exhaustive answer. Commented Feb 15, 2016 at 14:20
• This doesn't even attempt to answer the question. The two questions "this is correct" could correspond to are did OP overcharge the battery, and can he charge the cells separately. The answer to these are NO (cells are dead, can't charge them, and the issue is dead cells not overcharging), not "that is correct". OP has dead cells and a useless battery. Telling him how voltage works in parallel/serial configs doesn't help him at all, and actually OP seems to already know this info. Commented Feb 15, 2016 at 15:14