Laptop Battery Backup

Discussion in 'Power Electronics' started by EvilVargon, Sep 7, 2016.

  1. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
    My laptop is pretty power hungry and cannot last a couple of classes in a row. So I am looking into battery packs, however everything is incredibly expensive. What would it take to make my own battery pack out of say, 18650s? My laptop takes 19.5V and 6.5A. I understand I can probably just put 6 of these together with a few resistors to settle out the extra voltage, however I wanted something larger.

    - Are 18650s my best bet for a battery of this size? Is there a better alternative?
    - What kind of voltage regulator would I need to properly implement this?
    - What would be the best place to get the right size plug for a laptop charger? eBay, Amazon, Manufacturer, etc.

    Thanks for the help!
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Look at the battery pack model number, and look up its datasheet it will tell you its voltage, whether its lithium or nicad, then you can get a better replacement pack.
  3. AlbertHall

    Well-Known Member

    Jun 4, 2014
    A cheaper option may be to adjust the settings of the laptop to minimise the power consumption. Most have such options but can be a bit difficult to find. One is to use the minimum screen brightness you can.
  4. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
    I already do this. I switched to Ubuntu writing in notepad on airplane mode with the lowest brightness. Even then, the laptop lasts around 2.5-3 hours. That's might be enough, but for some classes I'll need to actually use the Internet. Stupid me for getting a gaming laptop for school.
  5. EvilVargon

    Thread Starter New Member

    Apr 4, 2016
    I'm not looking to replace the battery itself. I'm trying to make an external battery pack to plug my laptop into. My apologies if I wasn't clear in the post.

    What I did look at however was the power brick's voltage/current. Is that what I should be aiming for or should I be getting the battery's voltages?
  6. wayneh


    Sep 9, 2010
    The problem with an external battery pack is that it needs to be voltage-regulated. As they discharge, batteries sag in voltage. You can buy adapters for your car that convert ~12VDC to the ~19VDC for a laptop. That's essentially what you need between your battery pack and your laptop. But I think by the time you build a battery pack and put a DC-DC converter on it, you'll have spent more time and money than you wanted.

    My suggestion is to invest more time in finding a replacement battery pack. Sometimes you can get one larger than the original, and there are tons of aftermarket sources out there.

    Or, put your time into getting a different laptop. A gaming laptop often has just enough battery to get from one outlet to another. Wrong tool for the job.
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    Last edited: Sep 8, 2016
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
    Yes look at it. Or... think about the battery swap with a charged one idea.
  9. wayneh


    Sep 9, 2010
    I'm answering here so that your duplicate thread can be closed.
    It's not quite that simple. You definitely don't want resistors in the power path, since that will just waste power. And slapping batteries together may be fine for a flashlight but in this application you need to consider what happens if/when the cells are not well matched. Your system needs to charge and discharge safely to avoid damaging cells.

    I think most laptop battery packs use these cells and they're likely the most economical.
    You need a DC-DC converter that can meet the voltage and amperage specifications. This will take some shopping to find. There are many on E-Bay but I think your amperage requirement is on the high end compared to most of them. Something like this is close, but not quite right. Maybe this. You'll just have to spend time sifting through.
    This solves the power out to the laptop issue. It does not solve the battery charging issues.
    If you have the time to wait, getting it on E-Bay from China will be the cheapest option. You can probably get a 5-pack cheaper than a single plug. The bad news is that you may need 5, because of the lower quality. It's hard to say, but I'd try to get it wherever you are ordering other parts, to reduce shipping. I assume you're in the U.S.? The electronics supply houses such as Mouser, DigiKey and Newark will have many options of quality parts.
  10. tcmtech

    Well-Known Member

    Nov 4, 2013
    If it was mine I would just put the 6 18659 cell battery output directly to the 19.5 volt input and go with that.

    Reason being your laptop has all the necessary power regulation and control already built into it and 6 18650 cells in series is 24 volts which should be well within the working limits of the internal power control circuits working range being many of those laptop power supplies are not all that accurate or well regulated.

    If you don't care for that approach you can get a automotive power adapter unit that takes a 12 volt input and gives a 19 - 20 volt output and feed that with a battery set of multiple parallel sets of 4 in series to power your laptop.
    ronv likes this.