I happened to be given 7 laptops that were destined for the landfill. All of them came without DC power adapters. Realising it would take a long time to receive DC power adapters by mail, I looked around.

Looking through my excessive 5v - 12v power adapters I found DC jacks that fit each of the laptops and cut each of them off.

The laptops I wanted to charge all required 19v inputs.

I placed 5 18650 cells in series, soldered wires them to the DC jacks, added a diode to the positive end and checked with a multimeter to get a voltage around 19.5v (inner being positive and outer shield ground.)

However, once I plugged the batteries into the DC jacks of each of the laptops, nothing happened. Except for one laptop which consumed ~10mAh from the five 18650 cells, but that was it.

Is there more to a DC power adapter? Why do (good quality) 18650 cells not work for the job?

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    \$\begingroup\$ Are you certain the laptops only have two terminals in their charging jacks? Many laptops have a third terminal for charging negotiation/status/etc. \$\endgroup\$ – uint128_t Feb 21 '16 at 22:30
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    \$\begingroup\$ Try doing more measurements. Power bricks oc voltage, load voltage, your batteries load voltage \$\endgroup\$ – PlasmaHH Feb 21 '16 at 22:36
  • \$\begingroup\$ @uint128_t the laptop that consumed ~10mAh has a third cable for sense (some laptops can work without it), but the "Pentium I" has a simple connection with only positive/negative. This is difficult to troubleshoot, because it may be a problem with the laptop itself. \$\endgroup\$ – Hakkar Feb 21 '16 at 22:52
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    \$\begingroup\$ @PlasmaHH I could give that a try. I'd assume that under load the batteries would output at ~17v, but i would need to check to be sure. \$\endgroup\$ – Hakkar Feb 21 '16 at 22:57

Among others, many HP, Dell and Sony laptops have a third wire with which the laptop identifies that a proper charger was used.

It is often easier to charge the battery directly instead of going through the laptop.

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