External laptop battery pack


This little hack was sent in by [andrew], he built it specifically for the long flight from Australia to the US. The idea is simple, but I wouldn’t have considered it given the cost of decent D Cells these days. H put together a 20 D-cell power pack, a regulator to keep it at 24v, and an eighth inch plug to power up his old ibook.

Update: I goofed and left out [andrew]‘s name.

35 thoughts on “External laptop battery pack

  1. Firstly, he was flying TO the USA not from it. I have no idea what Australia’s aviation safety standards are, they may very well be different than the USA’s. Do you pre-clear US customs in Australia? I doubt it.

    Secondly, the baggage scanners at airports can detect explosives. If they see anything suspicious, they will have you take the item out of your bag and they’ll do an extra wipe test for explosives. My Xbox always gets the person with white gloves wiping down the console, controllers & carrying bag with that white cloth thing which then goes in the explosives tester. In Canada (and I think in the USA as well) they like to do that to laptops too. In Europe they just x-ray it and its fine, but they will swap Xboxes.

    I’m sure procedures in Australia and very likely the rest of the world are very similar if not identical. That being said, Americans are way too scared of tweezers… what the hell am I going to do, stab you to death with them??? OH NO!

  2. I know someone who flew from UK to Sweden and had to dismantle the Atari ST he was carrying. I hope this guy doesn’t have those D-cells taken off him, but I imagine the device looks a lot like a hollywood bomb :-/

  3. i like the idea, but I’d probably use something a little bit more rechargeable. my laptop battery is a 12-cell li-ion, so i reckon 24 ni-mh or li-ion cells and a regulator should do a good job. fancy it into a pseudo-cooling-pad kinda thing for style and rig up a dedicated charger and it would be a lot more practical.

  4. also for non-apple laptops, removing the battery pack while using a homemade recharger is very highly recommended, otherwise the dumb laptop tries to pull extra juice to charge the battery.

    i don’t think i could fly with such a battery pack… my workbench has gunpowder all over it. i’d use my battery for camping or blackouts or something.

  5. “20D energizers..” from Spike Lees film Do the Right Thing (apologies for the language) prelaptop/ipod ghetto blasting era:
    Radio Raheem: Give me 20 D Energizers.
    Sonny: 20 C Energizers?
    Radio Raheem: Not C, D.
    Sonny: C Energizers?
    Radio Raheem: D, motherfucker, D. Learn to speak English first, all right?
    Kim: How many you say?
    Radio Raheem: 20, motherfucker, 20.
    Sonny: Motherfuck you.
    Radio Raheem: Motherfuck you? You, you all right, man.

  6. very much a dirty hack. as the maker mentioned, it *did* serve his purpose, and the LM317 is dirt cheap. it is, also, ancient. as far as regulators go, linear is not the way to do this (hence the need for a huge heatsink). even with just linear regulators, the LM317 is ancient crap; a LDO (low-dropout) linear would be much better (course you’d still need a heck of a heatsink). this system is less than 66% efficient; with a buck regulator it could be over 90%.

    course, this was a one-off hack (he even threw the batteries out when he landed). a nimh pack with a buck regulator could be nice (minus the airport issues).

  7. carlton: you’re absolutely right. it was definitely a “dirty hack”. if i had intended to use it again I would not have used a linear regulator, and certainly not alkaline D-cells. i looked into a nimh solution, but the overall cost seemed to approach that of commercial external laptop packs, so i just found the cheapest D-cells I could find, and everything else I already had.

    as for the airport, i guess the australians just didn’t consider a 13-year-old caucasian american a security threat. i did pull out the battery pack and put it through security separately, and they were more or less okay with that. i really did scare a few other people, though, who backed away in fear when they saw all the batteries and wires :)

  8. first of all, when i saw the end product i was absolutely amazed that you got this onto a plane.

    good idea, if there was a commercial solution available for my laptop, i would buy one.

  9. It’d be almost 7 pounds, assuming one D cell battery is 150 grams.
    150 grams * 20 batteries = 3000 grams
    1 pound = 453.59237 grams
    3000 / 453.59237 = 6.61386787 pounds

  10. sometimes these quick and dirty hacks are the most rewarding… its great when a little work gets the job done :)

    Reminds me of an exercise in school where we needed an exact 1 hz clock pulse. Everyone spent hours finding the right resistors for a 555. I ripped apart a broken clock and in 15 minutes had a 1 hz clock accurate out to a few months :)

  11. Considering the watt hours of consumer grade cells this thing probably wouldn’t last an hour before needing a recharge, or cell replacement, and that’s being generous.

    Also Alkaline and NiMH current levels drop fast when on a heavy load. If you’re on anything over a P2 you’ll barely get a warning before the BIOS shuts your laptop down.

    I could be wrong though. I only considered the fact his possessor alone probably uses at least 32 watts, and that’s not even core2 duo or athlon 64. For example my antique thinkpad 380d(150Mhz Pentium) uses between 48 and 54 watts total depending on the work load.

  12. umm… tjhooker, you are absolutely wrong. are you accusing me of lying about how long i was able to use the battery pack, or did you just not read it? with power from 20 alkaline D-cells my ibook, which pulls 20 watts on average, lasted an entire flight from sydney to los angeles with power left to spare.

    furthermore those numbers for your “antique thinkpad” must be wrong. there is no way on this earth that “between 48 and 54 watts total” will be pulled by a functioning laptop running a 150MHz pentium cpu (which i’m not sure even exists — pentiums usually skip from 133MHz to 166MHz). most desktop cpus don’t even pull that much power!!

  13. #17 They don’t skip. The 150Mhz Pentium’s where in a lot of systems in the mid 90′s, they had MMX in some of them.

    My old thinkpad uses 16V at 3.37 Amps through the mains regulator output, it’s probably regulated in on the main board though. It uses 8.4V at 3.5 amps through the NiMH/Limh bus input. I’ll let you do the math.

    It’s highly likely you’re system is more energy efficient, especially in the LCD.

    I’m not saying it can’t work, just saying it isn’t very practical, even with rechargeable cells.

  14. Also #17: where you being serious about a 150Mhz system(whole system,) not likely to be pulling ~50 watts of power? Just out of curiosity have you ever built a system from parts you bought separately, or even looked at the power consumption charts on hardware vendor sites?

    It’s not that shocking, especially with a early model LCD based fully functional laptop.

  15. an Alkaline D cell would have something like a few thousand mAH so 500mA for a few hours is belivable (hell even new AA nihm’s are reaching 3000, that’d be 5-6 hours on a pack of AA’s), and computers rarely use anywhere near the quoted power levels on the manufacturers site, so, 20w is plausable, and likely true aswell, because that regulator isnt speced to do much more, was thinking how unsafe that setup was, due to the fact that if it did draw 30-40watts try and charge the battery or something, would likely have ended up smoking the regulator, and that would have been fantastic fun on an aircraft, likely caused a hell of a fuss.

    but yea, I think they are starting to make buck/boost regulators that are almost a slot in replacement for common linear regulators, think it was a project listed on this site only a few months back even that used one.

  16. a good d cell is about 18,000 mah on standard usage. using a lot of them in series with a regulator will both lower the total voltage and raise the amperage. i dont doubt this things ability to power a laptop for a long period of time.

    laptop batteries:
    8 – 12 a-size liion or nimh cells (~900mah each)
    this thing:
    20 d-size alkaline cells (~18000mah each)

  17. tjhooker: i find it very unbelievable that on average a laptop with a 150MHz pentium (so they do exist — my bad) will pull 50 watts because i have had many old laptops from that era and none have come close. and if you are simply reading what the ac adapter says that would be the extreme maximum as most systems will pull much less (#23 agrees).

    #21-#24, you are all correct in the power output of D-cells. i have no idea why someone would think that D-cells could not give 500mA for hours, unless, of course, they were thinking of heavy duty batteries or something…

  18. Once again my theory was/is that it isn’t practical, not that it wouldn’t work. The Duracell and Apple documents actually reinforce what I’ve said so far.

    A whole laptop, no matter the processor would pull in at least 1 amp. A 40+ Gigabyte drive alone is commonly .79 amps.

    I find it retarded, in a literal sense, that people think a whole system could not pull in 3 amps on a DC source even at low processor and I/O loads.

    To further stress my point look at the amp rating on any hard disk drive. Even setting idle it consumes most of that.

    This isn’t even complex math, simple addition of the idle amp ratings on hardware are all that’s needed.

  19. lol, this isnt about adding up amperages, as you cant add 5v amps and 12v amps and expect that to be a total, all depends on the internal power converters, switch mode psus as used in pcs and laptops, will pull close to a ratio of power depending on the voltage, so, with the 24v said here as the battery pack level, if you needed 5v at 1A, it would draw close to or about (5/24) * 1A = 0.2A at 24volts (+10-20% for inefficency).

    also harddrives use significantly less power when idling, the quoted power is usually slightly higher, and, has to take into account power needed to spin up, and power to move the head, moving the head randomly uses up quite a lot more power. (P.S. i have measured various drives with a Clamp meter at one point, also various power draw on the AC side of complete systems) most things will give a rating close to or exceeding the maximum expected power useage.

    Energizer quotes there alk D’s as having 20500mAH and Eveready SHD as 8000mAH, even the SHD should last over half a day constant.

    so, talking AMPS is useless, have to talk total power, hell, if you talk about the amps a CPU itself draws, its somewhere between 10-80 odd depending on how old / new, but you wont be seeing that current taken from the input power (considering AC sockets are only rated to 10A @ 240v)

  20. i thought the idea was to use less power to due the same work load. low power use. back light switched to led. hard drive to cf or solid state. low power usage via’s might be a way. make it cheap and robust.

  21. I have to say that it is unbelievable that a bunch of people on the interweb are telling someone else that he couldn’t possibly have done what he claims to have done.

    Like he really has anything to gain from lying to people online.

  22. I would like to apologise. I was blind and did not see the second page of comments and did not realise that this issue was resolved as it currently is.

    On top of that, it may have been snarkier then it should have been.

  23. all right, yea i think we’re pretty much done here. i’m not trying to start anything, but i thought i might add that right now i’m running an old 166MHz pentium tablet pc that’s rated for 16V at 2.5A on a regular ol 12V wall wart. the wall wart is rated for 1A max, and it isn’t even warm. it’s been like that for an hour. that’s 12 watts or *less* !! even i was shocked :)

    so, basically what i’m saying is that, from experience, the ratings on laptops are usually quite conservative. often you can get by giving them less voltage, and they’ll usually pull a lot less current than they’re rated for, too.

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