LiPoly Charger - Single Cell 3.7-7V Input

Replacement:PRT-10161. The MAX1555 was discontinued. We have a new version using a new IC. This page is for reference only.

This is a Polymer Lithium Ion battery charger based on the MAX1555 IC. This charger uses either USB bus power (MAX1555 internally limits this to 100mA) or 2.1mm center positive wall-wart power (MAX1555 internally limits this to 300mA). Current is automatically reduced to a trickle when charging is complete. Cheap, easy to use, and flexible, this board serves as a great demo board for the MAX1555. This charger is a 'must have' for quick and clean charging of Lithium Polymer chemistry batteries.

Check out this iPhone Charger!

  • Intelligent IC monitored charging - Constant current/Constant Voltage
  • Do not use this charger to charge NiMH, NiCd, or any other battery type
  • Comes fully assembled and tested
  • Single Cell Charger
  • Requires 3.7V to 7V(max!) Input
  • MAX1555 will automatically choose the wall-wart charging if both USB and barrel jacks are connected to power
  • Separate header for external power in
  • Separate headers for battery and load system so batteries don't have to be removed for charging


Looking for answers to technical questions?

We welcome your comments and suggestions below. However, if you are looking for solutions to technical questions please see our Technical Assistance page.

  • CAYESA / about 14 years ago / 2

    Is it possible to use with lithium batteries?

  • S4lt3d / about 15 years ago / 2

    Does anyone know if this will charge the 20mAh lipo battery or the lithium coin battery?

  • andruluvsu / about 16 years ago / 2

    This charger is awesome and just the right size. But whatever you do... don't attach the battery backwards. I did that to mine and was treated to a fizt and puff of smoke from the charging IC. Other than not being quite idiot-proof, this board is so awesome I've gotta have another one!

  • PeterP / about 13 years ago / 1

    The MAX1555 gets very hot when charging a 700mah single cell li-ion battery through the barrel connector off a 6V unregulated power supply (6.7V nominal). I have smoked two MAX1555s in this manner.
    Powering the board off the USB input solves the problem. I'm now charging off a 5V regulated USB supply. It takes a bit longer to fully charge, but at least I don't have to worry about it bursting into flames.

  • williams / about 13 years ago / 1

    As I bought this a week before you discontinued it, I would like to know if there was some other problem with it I should know about.

    • RyanEaves / about 13 years ago / 1

      I second this question. I bought 2 and one stopped sending voltage to the battery after a few hours. Is the replacement more reliable?

  • MrSinewave / about 14 years ago / 1

    I successfully created an in-system solar power recharging single-LiPo cell system with this unit and a solar cell that outputs a nominal 6V, 120mA!
    I have been testing it for a while and it works great (but charging via solar power is generally pretty slow.)
    The trick is that your solar cell must NOT supply more than 7V absolute max (and more than 3.7V of course), and it must provide somewhat over 100mA (100mA min is needed for charging to happen.) I used DealExtreme SKU 17440 for my unit.
    Be very sure by measuring voltage output from the solar cell when it's in bright, full noon sunlight. If it's under 7V and it's rated with >100mA output, then you're good to go. Solar cells will output somewhat different voltages depending on how much light they get.
    SYS+GND on the charging board goes to the Vin of your circuit.
    BAT+GND goes to a single Li-Po cell (I used the 2000mAh unit.)
    5V+GND goes to the solar cell.
    When the unit is in enough light, the red charging LED will illuminate to indicate charging. When light is insufficient, the LED will remain unlit. (The LED is also unlit when the cell is charged, so if the unit is getting enough light AND the LED is out, charging is complete.)
    Final note for anyone not familiar with solar cells: even dim sunlight is better (i.e provides more power) than just about any indoor lighting. So this is a by-the-window or outdoors thing, really.

    • Exploder / about 13 years ago / 1

      Thanks for the info!<br />
      <br />
      Then I'm curious to know how well solar charging works, and its safety. That is... I understand that LiPoly chargers like this one work by measuring the voltage coming out of the battery and then running through a cycle of putting the appropriate amount of power back in, eventually decreasing it to a tiny amount when the cell is putting out its max voltage. But if you're using a small solar cell that dips below 3.7V whenever the sun goes behind a cloud, and if it were to do so fifty times a day, is there any chance that this would trick the charger into going through fifty cycles and overcharging the battery?<br />
      <br />
      I'm guessing there's no chance of that, but it seemed worth asking. I'm thinking of building a setup like yours, leaving it out all the time, and using it to for all my power while on an extremely long bicycle trip. (So I also figure I should make a habit of disconnecting the solar and running the battery all the way down every once in a while to preserve its capacity?)<br />
      <br />
      Any experience or advice would be much appreciated.

  • Quinton / about 14 years ago / 1

    I purchased one of these along with the 300mA 5 volt step up board ( Item #8290) and the 2000mAh LiPo battery. (Item #8483)
    I used them to power an arduino and ethernet shield with a 5V 500mA wall wart. The intent was to have a UPS so the arduino could send updates even when power is lost.
    I completely charged the battery, it measured 4v with about 250mA when the load was applied and my program ran just fine for about 30 minutes at which time it failed. After the failure I measured the battery voltage and it measured 1.5v. I did the calculations and I should have had at least 6 hours of run time. I charged the battery again but after 6 hours of charging the battery only read 3.2 volts and after 10 hours the battery dropped to .15v and would no longer charge. I swapped in an older 2500mAh battery I had on hand, it went on to the charger at 3.3v and was down to 1.6v in an hour. The step up board works fine with another battery.
    Is my charger defective? Have I killed both of my batteries?

  • Pineapple / about 14 years ago / 1

    I "still" can't figure out the SMD LED.
    Is it lit when the batteries are fully charged ?
    Is it lit when the batteries are being charged ?
    I am trying to build the minty boost charger with a solar panel.
    Thanks for your help.

    • MikeGrusin / about 14 years ago / 1

      The LED simply indicates charging. When the LED is on, it's charging, when it's off, it's finished charging. Hopefully that helps!

  • HugoXP / about 14 years ago / 1

    What kind of component is "SJ1" represented in: "LiPoly/Lithium Ion Charger Schematic"?

    • jescombe / about 14 years ago / 3

      It's a solder jumper, between the USB and DC inputs.
      See the MAX1551 datasheet - joining this would allow you to pull 280mA from the USB connector, else it's 100mA (the maximum allowed by USB standard without any negotiation).

  • dongcarl / about 14 years ago / 1

    Can anyone give me some suggestions as to what remote LED to pick??

  • Yes. That is correct. The 'SYS' connects to where your battery would normally connect to your 'system' or your project. So you can charge the battery and power your device at the same time.

  • PJW / about 14 years ago / 1

    how would you connect this charger to the LilyPad LiPower 5V supply (DEV-08786). Is it from the center JST (SYS)of the charger to the JST jack on the power supply, is this correct?

  • Downgrade / about 14 years ago / 1

    Any one have any idea how worried I should be when I go to charge a battery with about a 6v input and it starts to make a high pitched noise? I'm using 2 sets of 2 garden solar lamp panels, I added a diode because they were making just under 7v and I didn't want to max it out.

  • JPristel / about 14 years ago / 1

    I bought 5 of these and after a week, three are still working, on one the status LED appears to have burnt out, but appears to be charging at roughly 50mA. The other one will slowly drain the battery at about 5mAh by illuminating the LED, but only when connected to a 5v power source. Don't waste your money on these, spend the extra $3 and get the LiPoly fast charger...

  • clearsky / about 14 years ago / 1

    What is the device called "SJ1" in the schematic? It's connected to USB_VIN and EXT_CHG

    • That would be a solder jumper/bridge; per the schematic, it shorts the barrel jack + input to the USB + input on the IC. As far as i can tell it's in case you have a high current output on your USB port (or a high current wall wart with a USB mini-b connection, commonly used by cell phones) and want to charge at 300mA on USB. That's my guess anyway.

      • crap, i just realized my mistake, ignore my previous post, that jumper goes between BATT & VBATT and disconnects the battery from the charge circuit.

  • testben / about 14 years ago / 1

    can this be used to charge the sparkfun 9v rechargeable li-poly battery (sku: PRT-09081)?

  • Exploder / about 14 years ago / 1

    Pardon if this is a dumb question - but suppose I put two 3.7V cells (of the same mAh) in series, keep them permanently connected to this thing, and charge and discharge them as if they were one 8.4V cell. I can get away with that, right? I'm not asking to catch on fire?

    • TimCole / about 14 years ago / 1

      It's not a dumb question at all.
      Do NOT try using this charger for two LiP batteries in series. The control circuitry for series charging is completely different.
      (Sorry if this has already been answered, but since it's a safety issue, I decided to answer right away.)

      • Exploder / about 13 years ago / 1

        Thanks, Tim!

      • tchilax / about 14 years ago / 1

        do you have any resources that you can recommend for working with lipo batteries in series and parallel? I would like to design a battery system that utilizes 3.7v 200mAh single cells in various series/parallel arrangements to increase voltage and maximize mAh. I would also like to charge the system with a standard usb port if possible. I know lipo batteries can be dangerous so I'm hesitant to experiment... can you help?
        Thanks for your time!

        • TLAlexander / about 13 years ago / 1

          I have an Eval Board for one of the TI bqSwitcher multi LiPo charging ICs. It will charge a variety of cell arrangements configured by jumper, and its easy to use. They are $50 on digikey and about the same size as the boards on this page. TI part number BQ24103AEVM.<br />
          <br />
          However, you generally need to have a charge input that is at least the voltage of your batteries, to to charge two cells from USB, you'd need a boost circuit.<br />
          <br />
          If you do PCB design, go to and use their power supply calculator, it's great.

  • guitarist24000 / about 14 years ago / 1

    Will this stop the circuit automatically if the charge on the lithium battery is too low, or will it stop it to prevent overcharging?
    basically is it idiot proof?

  • droc / about 14 years ago / 1

    the status light is no longer on while the system is trying to charge. is this a problem?

  • mlee / about 14 years ago / 1

    This charger charges well. I've used it with the 3.7V 1000mAh battery (PRT-00339) and after a full charge, it's at a healthy 4.2V, which is fine for my applications.
    However, the biggest problem with this charger it is extremely difficult to unplug the battery from the charger. You certainly can't plug in the battery in backwards, which is great, but it's really really hard to get out. I have to use needle nose pliers every time to carefully pull out the battery connector from the receptacle on the charger.

  • dongcarl / about 14 years ago / 1

    Just some questions,
    What are the holes that are in the two circles for?
    What do the light colors indicate?

    • thisupend / about 14 years ago / 2

      it is for a spot for a remote led (in a case)it does not need it as there is one on the board
      the led on the board is red single color

  • cnorrick / about 14 years ago / 1

    I need something just like this that charges NiMH batteries for a solar MintyBoost. Does SparkFun have such a product? Any other suggestions?

  • DHowett / about 14 years ago / 1

    I do not believe that this board's mounting holes are spaced properly for fitting the standoff pips in the project case. :(
    It's still a great charger!

  • ryan.barrie / about 14 years ago / 1

    I have a dumb question, this charges at 3.7 volts, right? Or does it depend on the input?

    • bsodmike / about 14 years ago / 1

      It can take an input between 3.7 and 7V as stated above.

  • malachiconstant / about 15 years ago / 1

    Does anyone know if I can add an additional LED indicator to show when the battery is charging? I'm using this in a box where you can't see the one mounted and I want to run something to the surface to light up when its plugged into AC or solar via the barrel jack.

    • bsodmike / about 14 years ago / 1

      You can desolder the on-board SMD LED and make a connection to your penalized LED. Would be a good idea to maintain similar forward voltages, when picking your panel LED.

      • thisupend / about 14 years ago / 2

        On the board next to the led is a circle printed around the header this is for a remote led

  • Blaster / about 15 years ago / 1

    does ny one know if you can put li-ion/lipo batterys in parrelel?

    • TLAlexander / about 13 years ago / 1

      You're not supposed to put LiPo batteries in parallel unless they are matched cells. This is usually done at the factory. So if you need more capacity, you should buy a pack with higher capacity, which will likely have cells in parallel inside.

    • mct75 / about 15 years ago / 1

      I don't think the max1555 does any DC-DC switching, so I would think you'd only get the 130ma.
      Also, unless the lipo cells have identical internal resistances, bad things would happen while charging and discharging them in parallel.

  • Blaster / about 15 years ago / 1

    hi, if i use this solar pannal wich is 5.5v 130mah will the charger charge a 2A battery at 193mah or will it only charge just the 130mah?
    5.5v x 0.130A = 0.715W / 3.7v = 0.193 = 193mah
    also is this ok to use on a Li-ion battery?
    also has any one cut the bord in half(only he clips off) to make it smaller?

    • TLAlexander / about 13 years ago / 1

      I know your comment is old, but just in case people are wondering: Yes, I have cut this board in half. Works great.

  • Rcrowley / about 15 years ago / 1

    The board appears to have three connectors for battery cells, but the Features list says: "Single Cell Charger"?
    Which is it? Am I missing something here?

    • AndySh / about 15 years ago / 1

      Take a look at the schematic or the zoomed up image of the board itself. One is to the battery, the second is to your circuit that is powered by the battery/charger, and the third is for the 5V that powers the charger.
      My personal suggestion is that if you get this board, you also get some of the JST mating connectors at the same time. This chip will let the smoke out (with authority!) if you plug in your Lipo backwards. The extra header holes are a nice idea, but when adding your own connector, definitely make sure they are keyed.
      Not that I would do something so foolish...

      • Rcrowley / about 15 years ago / 1

        Thanks, Andy. I was confused by the schematic which shows four connectors (JP2, JP3, JP5, JP6) all wired in parallel to "VLIPO".

  • Jared-70540 / about 15 years ago / 1

    Could you charge 2 LiPos at once if you connected the second battery to the system connector? I'm too affraid to try, heh.
    Also, Sparkfun employees, update your docs so it shows the new board please. 8) I've had this board for almost a year and the docs show the old version of the board STILL.

  • dimkasta / about 15 years ago / 1

    I doubt button cells are rechargeable...
    Anyway. I was wondering the same as Jody.
    I need my device to go on a low-power state to protect its oLed and maintain its internal clock.
    I guess I could add a simple transistor on the extra led sockets and simply signal the device to stay at low power state while the CHK pin on the MAX1555 keeps sinking current (charging).
    Do you think the

  • charred_water / about 15 years ago / 1

    Does the charger come with a wall adapter to charge from AC?

  • ralphzoontjens / about 15 years ago / 1

    Yeah I was also wondering if this board can be used to charge Li-ion button cell batteries. Anyone got any experience with this?

    • EricWertz / about 13 years ago / 1

      Be careful -- most button cells that taste lithium-y are "lithium" batteries, not "lithium ion" (or LiPoly) batteries. The former are 3V rather than 3.7, and are NOT rechargeable.

    • stuff dude guy / about 14 years ago / 1

      sure, but it hasvto be 3.7 volts, and Lithium Polmer

  • wasutton3 / about 15 years ago / 1

    hey i was wondering if anyone knew what the voltage and impedance for the capacitors on this board are. i am in the process of redesigning the board with something else so stay tuned

  • Jody Franklin / about 15 years ago / 1

    I've been looking for a rechargeable battery solution for a project, and am considering LiPo as an option. I like that this board is designed in such a way as to be installed in a device and leave the battery in place during charging, but has anyone actually tried using it that way? How has it held up to the device being active (in a low power state) during the charge cycle?
    I could just use the charge light to trigger a power down during charge, but would prefer to allow the device to operate (below the 300mA the charger will deliver) while the charge cycle is running.
    Would like to know before letting out the magic smoke. :D

  • RedLion / about 15 years ago / 1

    I have a couple of the older boards, the ones without the JST (?) connectors, and they work fantastically. I used them to build rechargeable MintyBoosts. One is in a standard sized Penguin mints tin and powered by a 2200mAh LiPo. The other is in a .5 ounce Penguin tin (~ 2.5 x 1.75 inches) and is powered by a 720mAh LiPo. They take forever to charge by USB and the smaller one charges my Android Dev1 to only about 50%, but they work!

  • djmanning / about 15 years ago / 1

    This board is just about perfect for many projects. It would be nice to have the USB data lines split out to a small header. One USB port to charge the lipo and send/receive data, even if the charge is slow.

  • Dragonos / about 16 years ago / 1

    It works but my battery got stuck in the socket and broke it of.
    Great charger though.

    • JayK / about 15 years ago / 1

      Same problem. I just got this in the mail and broke the connector first try. Even with needle nose, I can't get the remnants of the connector out of there.

      • TLAlexander / about 14 years ago / 1

        These JST connectors can be extremely difficult to remove! I've had a few that broke when removing.
        At work we use Hirose DF-13 connectors, which are similar, but I like them a lot more. They're a bit smaller, which is nice, but they are a bit easier to remove and reuse. Digikey also sells pre-crimped wires for like $0.50 a piece, which is what we buy at work.
        I really haven't been happy with the JST connectors.

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