How to Charge Lithium Batteries 

NO, NO, NO !! I'm an engineer who designs chargers for a living, for a fortune 100 company that you know. PLEASE do NOT leave the batteries on the charger when fully charged. When they get to 4.2v, you you start monitoring the current. When the current gets down to 125mA, you must REMOVE the supply. Otherwise, the electrodes begin to accumulate lithium metal on them. This clogs up the internal chemical structures, permanently decreasing their capacity by a small amount. This isn't the biggest problem. The biggest issue is that the lithium will demand to be set free, causing the cell to vent. Violently ! You can die, your house can burn down, and your insurance company will NOT be happy. If you want to keep them topped off, turn on the charger every week or so, and let them drink until the current goes down to 125mA again. Also, don't put more than 2 times the current into the cell, than it's rated capacity, or it will explode. The 18560 you had there must not exceed it's 2.5AH x 2, or 5A charge, no matter how hungry it is. Another thing, if the cell is really, most sincerely dead, with terminal voltage less than 2.7v, you can't safely let it eat 2x it's AH capacity in current. You must do a pre-charge. Limit the current to about 1/10th of it's capacity, or 250mA, until it reaches 2.7v. Then let it rest for about 5 minutes. If it holds the 2.7v, then you can charge it normally. If its voltage falls back, you can repeat this a couple or three times. If it keeps falling, it's done. Toss it. If it tests shorted, drawing max current for 15 seconds, it's done. If the cells heat while charging, to about 20 degrees above ambient, stop charging & let it rest. Only attempt to charge a cell if it's between 0 and 50 degrees C. You're right about single cells in parallel. They can be treated as one big cell. Each cell in a series string MUST be monitored individually while charging, to make sure they don't climb above 4.2v. If any do, charging must stop & the pack is unbalanced. Better chargers will try & match each cell in a string, to improve pack performance. The cells MUST be monitored individually during discharge. If ANY cells in a string falls below 2.7V, the pack MUST be considered depleted. If you discharge any string, such that a cell reaches 0v, the other cells will try & force current through it backwards. It will act as a load, and explode with great robustness. OK, that's at least $10k worth of consulting an analysis in engineering costs, free for you and your readers. Please heed my information, because I REALLY know whereof I speak. I'm not being an over cautious alarmist, despite what flamers may tell you. I have witnessed detonations in person. Please don't skip these instructions. Cheers, Randy

Mr Garcia, you obviously have lots of hands-on experience charging lithium battery. The important details left out are: Find those switching regulators which: - limit the voltage to some adjustable value (4.2 volt for 1 cell, 12.6 volt for 3 cells) - limit the current to some value specified in Amps - when current limit is hit, must not go in shut down mode, like most computer power supply do ; instead, it must continuously adjust the voltage to keep the current at the limit In other word, the power supply will start at the same low voltage as the battery discharge state. As the battery is charging, the voltage will raise while the current will remain at the fixed maximum allowed. When the voltage reach 4.2 volt, the power supply automatically enter in the second mode of operation, which is regulating the current to maintain that fixed 4.2 volt. The battery is still charging when reaching 4.2 volt, but it consume less and less current. It is really the battery that "decide" how much current it want, the power supply just try to keep the voltage at 4.2 volt and provide as much current as the battery want to keep that voltage. Now, to speed up charging, we want to provide a voltage slightly higher than 4.2 volt (or 12.6 volt for 3 cells). The extra voltage is provided to counter act the loss in the following components: - loss in wires - loss in connectors - loss in batteries The loss in wire can be decreased by using thicker wires. But bigger wires are more rigid, less flexible and get damaged faster from constant flexing. Typical cable in USB charger with a current of 1 amp waste from 0.1 to 1 volt. The loss in connector is often in the same range of 0.1 to 1 volt. Even when the exposed metal on the connector appear shiny yellow, imitating the look of gold, they may still waste part of the energy, which imply absorbing part of the voltage. Those bad quality connector become warm to the touch. The battery itself, particularly as they age, waste a portion of the charging energy. An old battery that waste part of the charging energy is exactly equivalent to a very good battery with a small resistor added in series ; both located physically inside the batteries. Let's take a real example : suppose the battery has an internal resistance of 1 ohm and we provide 1 amp of current. The ohm law allow to find the voltage across a resistor: V = RI = 1 ohm * 1 Amp = 1 volt The battery itself takes from 3 volt to 4.2 volt as it charge, and the internal resistance take 1 volt. We can also find how much energy is wasted by the internal resistance as follow: P = VI = 1 volt * 1 Amp = 1 watt Suppose that the battery charge level started at 3 volt and is now at 4 volt. Our charger is still pushing 1 amp since we are still below 4.2 volt. The total energy provided by the charger is: P = VI = 4 volt * 1 Amp = 4 watt The energy wasted by the internal resistance (assuming 1 ohm) is: 1 Watt, as calculated above Brief, 3 watts are used to charge the battery and 1 watt wasted as heat All the long text above is to explain what make a battery to become hot during charging. The lithium battery are strong when delivering high current, but they easily get damaged by silly little thing such as overcharging them or discharging them too much. All lithium battery designed by an company, not just professionals equipment, but every device (even the cheapest Chinese clone and the cheapest child toy) include a temperature sensor which is used during charging. The charger inside your cell phone does the following test: - refuse to charge if temperature already too high - start in fixed current mode, with voltage increasing slowly - monitor for "fast" temperature change with high precision (down to 0.1 degree Celsius or about 1.5 F) and stop charging if increase "fast" - while charging, stop if temperature exceed some threshold - when the voltage reach a limit, switch to fix voltage (the current is decreasing slowly) The end of charge is determined by: - current below a fix value while voltage already at 4.2 volt (for example) - temperature suddenly raise at any time during charging When the battery get old, it may accept less total energy and may decrease the maximum voltage to a value below 4.2 volt. By monitoring the temperature raise with high precision, the charger can stop charging and avoid damaging the battery. This precise temperature monitoring technique is what allowed old battery to keep working for many months after the voltage started to drop. Somebody got a patent for that and that company probably still get large amount of royalty for allowing all of us to use the same cell phone with the original battery for a few years. The battery exploding in recent Samsung cell phone is probably caused by an engineer who wasn't not very clever. He didn't read the patent explaining how to charge a lithium battery correctly and use the temperature sensor in a smart way.

Thanks Jehu, I find your videos both educational and entertaining :)

It's nice to know that multi-parallel-cell lithium packs don't drift much. For anyone wondering, it may be because the 33 parallel cells each have a different internal series resistance (which usually causes voltage drift), but as such a large number of cells are used, the resistance averages out to a common number (gaussian resistance distribution; one has a very high resistance, other has a very low one and the rest are in between), and each series group gets a similar resistance, making the pack accept the same charge. And, as example RC Packs are usually 1P (1 parallel cell), the resistance between cells is uneven, thus requiring leveling.

Dogs rule lol. One of my favorite channels, and this is a simple but yet very informative video.

Didn't realize how old this video was. I am thoroughly enjoying watching.

I know this is an older video but it's finding me perfectly on my path of learning electronics and batteries. Thank you!

this is a great video I have had a usable understanding of this concept before but not the total application of it till now. Thanks (i am recommending this video to my old high school tech teacher lol

Thanks for sharing your adventures, to include both your wins and fails.

5:22 I know someone has probably already said this but 4.2v * 2 = 8.4v dude :)

This is really excellent and filled in a few blanks. I now have upgraded a couple of drill to Lithium. An converted the constant voltage charger to cater for 2, 3 and 5 cells battery packs. As this is the most comment electric drill battery size! Works perfect

Excellent video. I've watched it 5 times so far and will probably watch it another 5.

Thanks man. This was really interesting and straight forward!

Always love watching your videos. One thing I wanted to point out, when you explained series charging, you said two batteries in series are not 4.2, they are 7.4, then you add another 4.2 volts for a third battery. People just learning how to do this don't understand or may not know that nominal voltage for these batteries is 3.7. If the math doesn't add up it might confuse them. Just wanted to let you know. Thanks

love your channel - really helping me learn on my current build !

Hey J First of all, love your video's, awesome work!!!! Keep it up, we love your attitude. I have been using a hobby grade "battery checker" something like the ones you use in your video's and after a balance charge on a high quality charger I have noticed a variance in cell voltages so I pulled out my recently calibrated Fluke Digital Multimeter, Just as I thought the cells were balanced perfectly but my "checker" was way off in fact both of my capacity meters were off. Just a heads up when doing benchmarks. Thanks again

Thanks man I never understood Constant current constant voltage properly before this was really well explained.

That's cool sir. It doesn't need bms, again its practical your doing great...

This is really useful info. Thanks for posting man!

Dude you are so inspirational to me I'm starting to watch all your videos and I just barely order things to build my batterie packs. 👍🏼👍🏼

new here and like what I am seeing. you are an inspiring creator. thank you for sharing your talents.

Dam, im just getting into this sort of thing and the first bit of this video was enormously helpful, you have yourself another subscriber.

Not quite the detail I was expecting as charging lithium cells can be a mine field. It's not quite as simple as hooking an 18650 to a wall wart, which some folk my mis-interpret. You really need a control circuit: TP4056 boards are good for testing this, and are abundant on eBay. They monitor the battery voltage and regulate current into the battery depending on charge state. Also bare lithium batteries without protection circuitry built in should not be charged unattended, cos if over charge occurs...well lithium fires are a bitch to put out!

Hello "J". Listen I had attended a Vocational H.S. and retired from the medical/medicine field and am able to follow, comprehend, technological trends and tech-info. I appreciate you willing to share with others what comes naturally to you. I suggest that, if you have something you want to share with an audience that may be unfamiliar/familiar, you write down exactly what you want to cover so that you don't bounce from one coincidence to another. Know your audience i.e. knowledgeable or novice. It gets a little schizo following your presentation: i.e. cover chargers-types-appearance-identify-connections-do's,don'ts-etc. Then cover batteries using the same approach. Avoid introducing terms, Sampo,? unless you initially introduce the item previously. Thank you would like to hear more.

What a refreshing change on Internet to find advice from somebody who knows what he's talking about. Believe me Jehucarcia, there are SO many who DON"T but that doesn't stop 'em! Thank you....Love the dogs...Only once a week to the park? Send me the air tickets..I'll do it for the rest of the week and get further training from you while I'm there. Thanks and good luck from Brexit land.

I am charging ALL my cells from solar. From the solar panels into step down converter. My cell packs are 21V and I have Step down set at 20.5V. Each cell has it's own protection circuit so will never shut off a cell. The series won't be broken. The series packs are 5 x 4.2V cells in series to give me 21V per pack. I then have 12 x packs in parrallel and then out to another step down converter to 12.6V for my home lighting. It is the prototype battery for my up coming TTPW (Tesla Type Power Wall). Videos on my other channel.

You are a blessing it pays to watch over and over your videos we are always picking up little nuggets hear and there some of us it takes a lot of repetition to learn and finally sink in thanks for your patience because of you we are up grading from L16 lead batteries to Li-ion John Morin in Milo, Maine 09-03 2017

Wicked! Thanks for sharing, I learned heaps by watching :)

Things like this video is what I’m talking about in my last comment …I learn something every time I re watch one of your videos ..learning about batteries is just my thing now thanks to you …🔋🔋🐐🐐🙌🏽🙌🏽👑👑

How much voltage is your battery supplier for the samba and how much voltage the motor works with? I have the same question for the amps as well... pls answer me them.

Thank you for sharing your precious knowledge with us

Hi Jehu, Thank you for the video, lots of fun! I understand the principle of slowly charging batteries for safety but I'm not sure about your charging. How are you regulating charging current which is a very important thing to do? Also have you checked individual cells to see if they balance out to relatively the same final voltage? How does Tesla, for example, charge a string of series batteries, is there concern for individual battery hogging? Also do they current limit? Thanks for your time, Rob

Hello Garcia,Could pls show us how to charge 18650 with buck converter specially emphasising on current control , like CC , CV etc issues. If u make a separate vid on it, wld be so grateful. Thanks for yr videos .:-)

BEST VIDEO EVER . THANK YOU . YUO ARE A BEAUTIFUL HUMAN BEING :)

Are you using fresh batteries for your power wall(or can i use laptop (recycled) battery for powerwall)

I learned something today! Well done!

Hi im just starting out with the Lithium Batteries and solar thing A big thanks for you're time and knowledge great info and easy to follow

Thanks for the informative video! So what do I need to buy to make a charger for 18v 18amph battery? (I'M trying to charge 2 m18 9ah milwalkee batteries in parallel without using the milwalkee single battery charger)

True! That would make a lot more sense! Thanks for clarification!

thank-you sir, a very good series to make some practical battery xp, it doesn't matter how much you read there are always some questions you basically resolved much of them, i have a request to make , i know its too late but if you make a frequency analysis of various chargers including expensive balance chargers, it will really help many people wanting a in depth explanation.

Excellent!! , enjoyed the session, as well as learing alot. Thanks.

It's been a year, did you see any difference in voltage and amperage since then?

How about charging a 3s or 4s battery pack using a desktop computer PSU? They're relatively cheap when on sale ($20-$30) and the 12v rail produces 35 amps. I figured you could use a bunch of imax b6 or another balance charger and connect them all in parallel with that 12v line. I've seen your open source balance charger but would like to know more about it.

Hey! I would like to say thanks for this video, it was very helpful! However there is one question came to my mind watching it. Why is it necessary for that 5KW charger to change the current while charging the battery on 126V? Isn't it enough to leave the battery pack to also reach 126V to know it is fully charged without decreasing the current, the same as a single cell reaching 4.2V to know it is fully charged? Can you explain this a little more please?

Now this is actually very helpful, knowing the potential difference between two points and how they interact with each other will help me avoid dangers. this explanation expanded my knowledge on the topic, tho we have to read R Rho's comment too it seems he has pointed interesting things out that might actually be dangerous.

I started pulling my hair out when he said 4.2 × 2 is 7.4.... twice!! Twice??

VERY Informative! I'm planning to convert my NiCd batteries for my old Milwaukee 6024 drill. Thinking, 6 in series will give me a total of 21Ah with a max of 18-20v through a voltage regulator and a low threshold cut off circuit around 3.4 before they become unstable. Possibly may use a thermistor and voltage display panel(just for the curious folks). What do you think? May even be able to squeeze more in the old case and bring the Ah up. Thanks.

As i saw in your video about the tesla wall, u used different batteries in it, so does it metter when they are connected in series or parallel for charging them and will it help the batteries to due quicklier?

Thank you very much Sr Good Afternoon

What if your PSU can output very high current. And now if you charge a lithium-ion cell that is empty. I always heard they need constant current, constant voltage. Can something bad happen, when there are to much amps going into the cell?

Nice video my knowledge is nada, now I'm starting to understand something (series and parallel). Do you have a video showing the samba construction ?

any chance of a video on choosing a BMS and what to look out for, what you need or don't need. great informative videos as ever.

I have been watching a few of your videos and I like the theory and learning of it all. I have a question, I am building a camper van and want to have the coach / house battery be lithium to supply power to my 12v items such as fridge, lights, fridge etc. My question is would building a battery pack out of the 18650 batteries at 12v work for this application? I would like to have storage of about 100 amp hour possibly 200 amp hour, so i feel this would be similar to the tesla power wall to power my van, i would also like to charge the batteries from both solar and the alternator while i am driving, as far as charging via the alternator is there any thing special needed to charge it from that i know of the sterling battery to battery chargers however pricey but the other option is a ACR type relay but would that cause harm to my lithium battery pack giving it different volts or the battery demanding alot of volts from the alternator.

Thanks,enjoyed your video. I just started watching your video's, they are very informative and interesting.

What’s that thing called that you plugged the bms wiring harness into to read the voltage?

Hey man thanks for great content man just took up an interest in batteries an your video are dd best on RU-vid you got my subscription

The battery guru. Thanks a bunch for the videos they are kick ass.

4:25: Dog's like, "C'mon, man, you said we were going to the park. Let's go!"

Hi , Can a adjustable power supply be connected directly to solar panels and then to battery bank? great vids ,.. thanks

5:35 4.2x2 = 7.4? I think it's 8.4 ..... I'm new to this and I wanna learn more about setting up batteries please lemme know if voltage drops in series

I learned so much! Thank you

Great video (as usual). Thanks

What fuse did you use with the individual batteries? Do you have a specific web page that shows the exact part numbers?

Hi, thank you for your video. I have a similar situation and a question on battery charging. I plan to charge my 72v 100AH Li-ion battery bank using a diesel generator which provides a regulated DC 72v 70A. Can I connect it directly to my battery bank, or do i need to buy some kind of a charge controller? If yes, would a solar charge controller would do the job, or I need some other controller? best regards!

i always enjoy your videos 💯 thank you so much

Thanks for your great postings. Im in Australia. I’m going to install 12v 240v 3000w Inverter with 12v 100ah Lithium Battery in my car. I’m trying to find a way to charge the Lithium Battery from 12v (120w) Lighter Port on dashboard directly in my car without connecting with my car battery if possible. Can you tell me what kind of stuffs that i need to buy from like Amazon?

Very tidy explanation. Thank you.

How you keep your batteries in that 2.5 - 4.2v without a bms.?

Hi, I have one question, I made 5 cells in parallel and 3 groups in series to be 12v pack and I agree with you to be not use the BMS to charge my pack so should I charge it with 12.2v cv/cc power supply or separate to 3 of 4.2v cv/cc power supply ? thank you.

I would add to the many good comments and tips posted already, BMS are pretty cheap now, esp. for a DIY'er and if you can't attend and monitor charging, a BMS can add the safety you need with lithium batts cutting the power when it's set V is reached. some also can set a flat timer for charging

Hi. I would like to know if you wanna balance that pack how you do that? with bottom or with top balance?

Great video can I ask where you got the battery box from as its perfect for a project I have to do,making a 24v golf buggy battery for a disabled friend

jehugarcia, YOU HAVE A GIFT FOR TEACHING!

I know it's been a while since you put this up but I have a question. I have a tp4056 single cell charger but I have made a 3s3p module. How can I set it up to charge as a 9p module and function as a 3s3p module without having to rewire it every time I charge it?

How to solder or weld lifepo4 32650 battery. Your information will be very helpful for my work. Thank you

I have 2 lifePO4 12v 8Ah I bought the first of this month. I bought a charge you have to set type of battery number of cells, voltage, etc. I tried to see the charger work. When I hook either battery up and try to start the charge I get a cell warning on both and no charge. My other charger gives me a cell balance problem. What do you think? I just got one of the Miady 20ah batteries today. The charger is at my office so haven’t had a chance to try it with either charger.

9:51 so you charge at 12V, but at what amps? Seems using 0.5-1.0 amps would be painfully slow... What's the recommended ratio of charging amp to total Ah/capacity?

Niceeeeeeee! this is very cool insight. I would never thought you would charge your battery pack of the samba electric with such small charger and powered by 99 cells

Very informative thanks..

What kind of tape do you use to tidy up wires and connections?? Does it have to be like "fire retardant" or the such??

Excellent education Jehu. Thank you. I NEEDED that.

what can u put your batteries in to charge them with that I'm using magnets to keep them together but because of the connection issue I lose a lot of mah on discharge

Exactly what I was searching for 🙏🙏🙏🇳🇬

Do you have a video on how to build a 12v lithium battery pack to replace a 12v sla battery in a battery booster? I have a couple boosters with dead batteries and a couple dozen 18650 cells laying around. Thanks.

Are those "Linear" converters your using to charge the Batts ?

I have two questions.i just build a 3s battery pack with balance charge cable (did not put pcb) total 12 batteries .My first question : 1)is it ok to use the battery pack without pcb? what should be my minimum voltage to stop using the pack? My second question is: 2) if i try to charge multiple cells lets say all of them (12) but each cell have different amps (capacity).is this safe? I know its not the best (pack will not perform as it should). Will all of those cells reach their real capacity when charging finish?(i have a turnigy when charging).what i understand from you is that turnigy will keep giving 12,6v to all the cells and 0,5amps(my charge setting) untill every cell is full.thanks and sorry for my bad english;)

So where do you get your batteries and what's a good price for the 18650's?

Hi jehugarcia: I am getting things together for a powerwall as in my area in Michigan I lose power in the home 2-6 times a year. I want a way to charge the pack and would like your recommendations on a way to charge it. Solar is not in the near future due to cost and efficiency here. What I would like to do if possible is run a small gasoline engine/alternator combo but have read this may be a problem getting them topped off. Can I power a solar charger with the engine /alt that may be the answer? I would really appreciate it if you could give me your recommendations for a solution to this question. I thought I saw a video of an earlier Samba trip your took and used a similar charger but didn't see what I could do to assemble one. Thank you for your solutions and videos answered on the tube. Of course I would need details as this stuff is all new to me.

hiii jahu... i need a battery of power 1kw... can u pls tell me the arrangement and the num of batteries required and about the other accessories or equipment i required

Wow great video just what i was looking for

What battery spot welder do you recommend?

Hey great video. I need to charge a 10 cell 18650 battery pack. How can I modify or use a cheap 24 volt laptop charger that pushes 6 amps to charge the pack. The pack already has a BMS so i dont have to worry about overcharging.... any ideas?!

So... If I want to charge 3 cells connected in series and another 3 cells (same series connection) with the 2 groups connected in parallel, and if each cell can except 1.5 amps, how many amps would I need to charge all 6 cells?

Screw all that lol where can i buy one of your batteries 24v 30ah send me a link need it for my lead acid skateboard trying to convert to lithium need a smaller lighter alternative please help

I learn a lot in this video,thanks

I have a e-bike battery it’s lithium ion it has 36 cells in it they’re packed in groups of six I believe one of the groups of six got disconnected, the weld connection broke so that group of six is lower voltage than the rest now the entire thing won't charge can I simply just re-weld it to the rest of them and charge it back up to normal or do I have to take them out separately to charge them up fully to match and then reconnect them??

What charger are you now using for your Bus? You say you use one of those power regulators for charging your 12 volt battery. I don't see where these are able to take in your pack voltage then derate to 12 volts? I see they take 120 AC volts. Do they also take 120 DC volts that you can then derate to 12 volts?

Good stuff... I think I'm going to quit explaining this stuff myself, and just que up your vids to do that job. I'll just answer questions afterwords. I usually set my chargers at .5c per cell, just to be safe. The exception is my E-cig (10.8Wh), which I charge at .8c. The E-cig stays cool, but the charger gets nice and warm.

I am using chev. Volt batteries to power my golf cars. I would like to use the chargers that come with the cars .Is this power supply that you are talking about the way to keep from over charging my battery? We are using 2. 48 volt packs wired parallel And then to the car. My charger can put out about 20amp at 57 volts, and the goes down as the batteries go up. If this is the way to go ,do you have specific power supply you would recommend for this application.

hi Jehu! help me out. If i have a battery pack of 3s33p around of 50ah, what is the max amp i can put to it? and send a voltage of 11.1. thanks in advance. And your channel is awesome