No Script, No Fear, All Opinion
RSS icon Home icon
  • EEVblog #176 – Lithium Ion/Polymer Battery Charging Tutorial

    Posted on June 9th, 2011 EEVblog 38 comments

    Want to include a small Lithium Ion or Lithium Ion Polymer battery into your next project? It’s easy! Dave gives you the low down on how they work and how to charge them and select a suitable charging IC.

    NOTE: For safety you should always use circuit protected cells as per the larger cell I was holding up. It protects against over-discharge, over-voltage, shorts etc.

    (BTW, the reference to Lithium Ion Polymer being the same as Lithium Ion is in terms of charging, if that was not clear. The Ion Polymer type have polymer anode material and hence a different construction that allows the small pouch type cells shown in the video, and other thin odd shapes shown toward the end)

    Be Sociable, Share!
    • PJN

      This is extremely interesting, thank you.

    • Wartex

      Dave I think you are way over your head on this one.

      There are MANY, many modern LiIon chemistries that do not follow your Manganese oxide or Cobalt charging guidelines. Take iron nanophosphate batteries which have 3.6v nominal and 2.5v discharged states – they are LiIon but have totally different behavior. Also, batteries that have been drained significantly (0.5v or more) below “dead” voltage will not take any charge, including “rejuvenation”. Once you drain it dead, you start an irreversible chemical reaction and that’s why any half-decent charger would refuse to charge a dead cell. Chemistries that will accept the low current boost will actually vent as soon as high current mode kicks in and either trigger a built-in PTC (in cylindrical) or vent and burst into very hot flames. This is where iPod/laptop fires come from – overdischarged LiPO sacks burst into flames due to poor BMS design.

      This is a useful tutorial, but you omitted the part where users *require* a low voltage cutoff as a part of BMS (battery management systems) otherwise you kill your cell on first discharge. BMS is an absolute requirement in modern LiIon applications, especially in multiple-cell applications where you need balancing. You can get away with charging manganese spinel cells such as eMoli or Samsung SDI 18650 in series, but most others will get unbalanced quickly and fail or cause fire.

      I can see a lot of LiPo fires and bricked cells coming as a result of this tutorial, you missed a crucial detail. LiIon is very unforgiving and dangerous, it’s not anything like NiCd.

      • EEVblog

        Geeze, I can’t cover every detail and every battery type and every design scenario in the one tutorial.
        Yes there are other Lithium Ion chemistries out there with different voltages and requirements, but by and large the batteries people are going to use will be standard 4.2V Lithium Ion or Lithium Polymer chemistry I covered here.
        (Digikey have 2000 device options at that level for a reason! Guess how many support 3.6V LiFePO4 ?, about 36 or so…)
        If people blindly follow my tutorials and don’t read and attempt to understand the datasheets and technology for the particular devices they are using then I can’t help that. I’m trying to give them a starting point in terms of charging these things, you have to start somewhere.
        Yes, completely discharging a cell can ruin them irreversibly, and good LiIon charger BM IC’s will cater for that, as will batteries with built in protection circuitry.
        Low voltage cutoff design probably requires it’s own tutorial as it’s not just applicable to Lithium Ion batteries, it’s part of the design process of any general battery powered design. But yes, I should have at mentioned it, I forgot. As I should have mentioned the cell with battery protection I showed.
        And BTW, with proper charger chips like I was showing the high current charge mode doesn’t just “kick in” automatically, it only does so if the cell is able to accept charge at the lower safe rate in certain amount of time, something that cells only capable of being rejuvenated safely from a low state can usually handle. Otherwise it doesn’t do the fast charge and cuts out. That’s why I’m trying to teach people to use these proper charger IC’s.

        Lithium Ion battery design can be an incredibly complex field, and there are many things I did not cover. But you gotta start somewhere.
        You are more than welcome to post a follow up video.

      • hpux735

        Though he didn’t make it explicit, like Limor did in her tutorial,

        I’m sure that Dave was expecting people to use only Li cells with built-in protection circuitry. This makes the low-voltage cutoff mostly a non-issue. Of course, you will seriously degrade the life of your batteries if you always hit the protection low voltage cutoff, but you’re unlikely to have a “vent in flame” event.

    • Alex

      Nice video on the subject! Learned some interesting aspects of this that I wasn’t aware of :)

      One thing I was slightly surprised didn’t come up, was the aspect of safety of lithium ion batteries, such as how some come with protection circuitry and some don’t. I’m guessing such topics didn’t come up because there was focus on the smaller capacity ones with less risks perhaps?

      • EEVblog

        Yes, that’s a whole other subject entirely I think – larger and high capacity battery pack design and charging, and protection and safety.
        This was meant as a tutorial on small capacity batteries to power your little low power gadget and charge it properly. Not to design battery systems for bleeding edge production electric cars, laptops, and RC gear etc
        One battery I showed had protection circuitry built in, I should have mentioned that.

    • Tom

      Nice one Dave.

      Ladyada did a similar tutorial not long ago, the two complement each other nicely:

      • EEVblog

        Didn’t know about that one, thanks.

    • JRR

      Thanks. I was thinking about using LiIon for my next project. This will help.

    • tchicago

      Hi, Dave, thanks for the video –

      This larger battery you mentioned, that comes with the builtin protection circuitry. Do you have a datasheet URL of it, especially the protection circuitry part? What’s the common functionalities of such builtin chips?

      • EEVblog

        Here is a typical protection PCB. Any decent battery supplier should be able to sell you protected cells with circuitry like this.
        I was thinking about a separate blog on this actually.

        • Khan


          What are the small circuits that are present on almost all of the Cell phone batteries ? I guess they are called protection circuits (Not Sure).

          What do those circuits do ?

          > For a typical application say making a simple torch, can i just use a cell phone battery and use the +ve and -Ve terminals from the cell phone battery to power the LED driver circuit and use the same terminals to charge the battery ?

          > Would the circuit on the battery prevent the battery from complete discharge ? or i would have to add another circuit to sense the low voltage ?

          > And Would this circuit on the battery prevent / cut off once the battery has charged (Can i use a 5V adapter to connect the Battery +ve and -ve respectively) to charge it ? (The battery in question is cellphone battery Motorola BT90 the ones shown in here 3.6V – – Please reply. Thanks -Khan

        • Laptop Batteries

          Thank you, Dave, this is a very good article physical processes explain the lithium-ion battery, and learned how to charge, in order to better protect the lithium-ion batteries and our equipment

    • Michel

      Hi Dave,


      This website also contains some useful articles about Li-ion batteries:

    • elektrinis

      Thank you Dave. Very useful video indeed.
      Now I’d like to see a video on BMS for large battery packs:
      low voltage cutoff, over-voltage cutoff, balancing methods (bleeding, energy transfer, etc), state of charge calculations and prediction, state of health predictions.. etc..

      I am interested in electric vehicle packs (I work in this industry), but smaller ones (multicell) will do OK.

      BTW, I use A123 LiFePO4 pouch 20Ah cells and a DIY BMS in my electric scooter (conversion):
      (The language is Lithuanian and I doubt it will make any sense, so sorry for it. But pictures tell many words)

      Every cell in this pack is able to charge in rate of 4C (15 minutes dead to full) and allow a long-term discharge current of 30C (600 amps, 1000 amps for 10 second bursts). Declared cell life is over 20’000 cycles and 20 years of calendar life. If used properly.

      For more info on the project check out my blog.

    • elektrinis

      Also, to see features of a modern BMS please check my company’s website:

    • magicmushroom666

      What i dont understand still is how the project on the end of this works. When you first connect the dead battery, and during the first charge cycle, the voltage will be rising slowly, surely that’s going to cause trouble for the LDO etc?

      Or is there where the battery management comes in? ie you couldn’t just use the circuit shown above, but need something in between, to disconnect the battery from the LDO while its charging, and power the project direct from the supply?

      Thinking about it, wouldn’t the regulator need to be before the charging IC to give it a sensible supply from whatever transformer etc is connected?

      • EEVblog

        This is only a simplistic example. The product obviously won’t work until the LDO reaches a suitable voltage.
        You would also design your product so it has some form of voltage cutout (often built into the battery itself). Draining and attempting to rejuvenate a dead cell is not normal operation, you’ll just damage the cell. It’s only there for those worst scenarios.
        Some chargers have battery management capabilities built in which handle these scenarios in any way you like depending upon how you want your product to perform under charging.

        • ton

          One interesting nicad battery charger I’ve seen has interesting settings:

          Refresh & Analyze: Charges the battery, rest for one hour, discharge, rest again, then recharges it. Selectable charging and discharging rate.

          Suitable for batteries stored for more than two weeks but less than 3 month or those showing poor performance.

          Break-In: Also known as IEC capacity measurement and “Battery Forming”. Charges battery at 0.1C for 16 hours, rest for one hour, discharges battery at 0.2C, then recharges again at 0.1C for 16 hours.

          Suitable for new batteries and those stored for more than 3 month.

          Discharge: Discharges the battery at the selected rate.

          Cycle: Performs charge-discharge cycle for up to 12 times with discharge capacity stored in memory. Recharges battery after final cycle.

    • mauimart

      Here is a chip I discovered while disassembling one of those mini RC helicopters. It handles both charge and Low Voltage Cutout. Probably not the best chip when it comes to maximizing cycle life of the cell.

    • trevor

      Regarding the x-axis or the capacity of the battery..

      Why is the second constant voltage phase depicted as having with same width as the constant current phase.. I thought the second phase charging accounts for only 10% of the capacity? Is it because the last 10% takes the same amount of time to complete as the first phase?

      • EEVblog

        Yes, the X axis is not to scale. I took some liberty there to show the concept and try and not cramp everything on the small whiteboard.
        I indirectly mentioned that, but should have made it clear.

    • TopherTheME

      Nice video Dave. If you have the time, I might suggest doing a short “sequel” about charging Li battery packs (serial||parallel configs). Things like cell balancing becomes very important when stepping up to higher power cells.

    • ton

      So how does it work if you have a pack of cells?

      Each charge management ic is looking to charge one 4.2 (or 4.1) battery, but if you have a bunch in series (for a 9v application for example), how can the charger work?

      • TopherTheME

        It depends on how you want to charge it. You can charge a string of cells in series by just applying a higher voltage across to + and – terminals in the pack and it will charge. However, unlike most other chemistries, Li batteries don’t have an auxiliary chemical reaction for when the battery is being overcharged. When a Li battery is over-charged the cathode is oxidized which is an exothermic reaction and can create a thermal runaway event, where as NiMH or SLA have an oxygen cycle or other proprietary reactions to prevent this. So if you have one low capacity cell in series with other high cap Li cells, you’re in trouble.

        The alternative is just to charge each cell individually to the same voltage, also referred to as balancing.

    • TopherTheME

      BTW Dave, there IS a difference between Lithium Polymer and Lithium Ion. As far as the typical end user is concerned they can be considered the same, but there are differences in the electrolyte and manufacturing processes between the two technologies.

    • billt

      I’d love to see some information about using and charging laptop battery packs. Do the packs contain charge control circuits? Do I need to provide that? Does something need to be both places? Or different things in each place? I’d like to repurpose an old laptop shell/battery that I don’t use anymore, replacing the aged battery ppack if needed, but to be able to continue using the laptop shell without a power tether line. But of course want to plug in and recharge properly.

    • negative scanner

      Thanks for this great blog, its amazing. I really appreciate you for sharing this information with us

    • Anonymous

      Thanks for this tutorial.

      If I want to charge two 4.2V batteries in parallel, can I simply “model” them as a single 4.2V battery but with twice the current capacity as a single cell? Anything I should watch out for?

    • WestfW

      Any thoughts on this circuit that has been floating around the RC community for some time: ??

      • kikkoman

        yeah, why not? like Dave said, it’s actually pretty easy.
        you can even use 2 LM317s (or similar) and a handful of components – one limits voltage, the other limits current. that’s all you need. there are a lot of DIY circuits like that.

        the only real downside is that there’s no termination, it simply approaches the voltage limit. so don’t forget to unplug the cell (or better yet, measure charge current).

        a few things I’d like to add: don’t blindly rely on a protection circuit unless you exactly know what it does.
        some allow overcharging – i’ve seen consumer products go up to 4.3..V which drastically shortens the battery’s life.
        some cut off at 4.05V or so which is good for the battery life but reduces capacity and – depending on the type – can confuse some chargers.
        likewise, don’t rely on the overdischarge “protection”. 2.75V, which is pretty common, is WAY too low.

    • Pingback: Smartphone battery life span - SitePoint Forums

    • Pingback: » Blog Archive » Links for Beginners in Electronics

    • Pingback: Polymer Ion

    • Daniel Lawton

      This helped me finish a design. I was just about to upgrade a supercap RTC backup, because TI’s AM1808 is a power hog on the RTC (17uA). We had an external RTC from davicom before, it was 1uA. My supercap wasn’t big enough anymore.

      I might have just stuck an “ultracap” on there, if I didn’t run into this. I saw the charger ICs, but their datasheets tended to be sparse.

    • Stuart Clark

      Nice one Dave,
      I appreciate your effort which is shown in your blog content. It’s new information for me the charging tutorial about Lithium Ion Polymer Battery.

    • Asphalt 8 Hack

      This page certainly has all of the information I wanted
      about this subject and didn’t know who to ask.

      Look at my web-site; Asphalt 8 Hack

    • Ifthekhar

      it is a very useful tutorial,recently i decided to build my own Li-Ion battery charger.I have one question and it may seem silly to you.
      While charging the battery in consent current, what should be the charging voltage?Should it be equal to the rated voltage of the battery or greater than that and while charging at constant voltage what should be the charging current current,0.5C or 1C?

      Thank You