What are the best options for building my own battery pack?

Dinesh kumar March 3, 2015
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Hi….

I am designing a power bank on my own now as my project.  I am finding it difficult to select a rechargeable battery of 2500mAh.  Should I choose Li-ion or Li-poly?  What are the batteries used inside the existing power bank models?
Also which 18650 battery has the longest life?

  1. Jack
    March 11, 2015 at 3:36 pm

    This sounds like a student project. I don't think issues like his "production" methods apply. I'm not even sure it's right for us to be answering.

  2. Justin
    March 4, 2015 at 5:16 pm

    I suggest you search Battery University and perhaps even join!
    More information there than you would ever want to know.

  3. ha14
    March 3, 2015 at 10:38 pm

    little difference between ion and polymer, polymer batteries are slimmer and lighter. If you are always on the go, the more mAh the better, also Lithium-ion Battery are more subject to aging, even if not in use (storage in a cool place reduces the aging effect).

  4. Jan F.
    March 3, 2015 at 5:47 pm

    I am somehow not at ease with this question because you make it "sound" so easy about you designing a pack yourself.

    Have you thought about how you are going to charge your makeshift pack? There are specific charging voltages you have to meet otherwise you will either kill your cells or it's a fire hazard (often described as explosion). You also have to make sure that they never go below 3V. Below that they are pretty much unrecoverable dead.

    Physical safety against leaking batteries and mechanical damage. If you physically damage (hit) a LiPo/LiIon battery it may just go up in flames too.

    A power bank is more than just a couple of AA batteries slapped together in a plastic casing with a USB (or other) connector.

    • Dinesh kumar
      March 4, 2015 at 10:41 am

      Thanks all

      I am designing the power bank with SoC ACT2802C as my academic project. Any suggestions about its circuit design will help me more. I am able to find only the datasheet and application notes in websites. Can anybody share a link where I can learn more about this power bank Design????????

    • Jan F.
      March 8, 2015 at 8:52 am

      The ACT2802C is a "fully featured" battery manager IC so it has most of the required circuitry build in.
      The good news is that you can basically do all of the necessary things with this chip.
      The bad news is that it will be harder to provide you with actual "circuitry" or PCB layouts as they have to be specific for this chip then.

      I would suggest starting with the datasheet as it already provides some basic circuitry examples .
      http://www.active-semi.com/sheets/ACT2802_Datasheet.pdf

      You can find a working example in the demo board sheet
      http://www.active-semi.com/sheets/ACT2802C_Application_Notes.pdf

      The demo board features USB output (for the device) and Micro-USB input e.g. to charge it from a USB wall charger or USB port on your computer. All that is left is attaching the actual battery.
      It's a double sided PCB ~ if that is not an option in your production I'm afraid you have to go back into Eagle (or whatever you are using) and think about the layout.

  5. Oron J
    March 3, 2015 at 4:54 pm

    The main difference between the types is that Li-Polymer is a lot less susceptible to spontaneous combustion, at a slight drop in storage efficiency. As such, I'd suggest that it would suit your purpose better (and indeed, is better for most uses). You can find a lot of useful information on batteries at http://batteryuniversity.com/ .

  6. Bruce E
    March 3, 2015 at 4:37 pm

    If you are looking to power a motor or other devices that require a higher discharge rate from the power source, you should be looking at the polymer batteries. The polymer batteries also tend to last longer and are safer in general.

    Since you are going to be using them in a battery pack, you need to make sure you are not using protected cells because the protection is based on the voltage of a single cell.

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