I started this project because my son lives on a rural farm block that has no mains power and needed an alternative way to reliably power his Compaq Presario CQ60 laptop.
He loves Puppy Linux and his main focus is using Librecad so I have tailored several Puppies to have Librecad built in - as well as Chromium Ungoogled which seems to be a very good browser for our usual needs.
- CompaqOnOzitoPower.jpg (118.37 KiB) Viewed 511 times
Shown here is my most recent version, based on Dpup Stretch 7.5 - powered from an Ozito power tool battery which is referred to as "18v" but which in reality varies from 20v when charged to 16v when its' internal BMS switches off the output.
This output needed regulating to match the laptop's requirements.
The laptop needs 18.5v and has an "intelligent" power plug that has the centre sense wire that is typical on Dell, HP and Compaq. As well as converting the battery output to a stable 18.5v I had to use a small adapter to convert the 2 wire 18.5v output to the 3 wire "intelligent plug".
Using this setup he can plug in the Ozito battery and run for an hour or two - then unplug the discharged Ozito and replace it with another fully charged one and continue (with the internal laptop battery picking up the slack during the Ozito battery swapover). He charges 6 Ozito batteries at a time using 3x dual fast chargers running from a small petrol generator. It takes about 70 minutes generator time to charge the batteries and he runs a small toasted sandwich maker while running the gennie 
(He also uses these batteries to feed 12v DC/DC converters to provide power for lighting and usb device charging such as cellphones etc)
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Here is some further detail:
- Components.jpg (161.24 KiB) Viewed 511 times
Item 1:
4AH Ozito powertool battery (Based on Lithium cells). Ozito is a cost effective Australian "DIY" range sold by Bunnings - but despite being "cheap DIY" the batteries are surprisingly reliable, being based on the German "Einhell" brand.
Item 2:
"3D printed" clip on adapter sourced from AliExpress. I fitted this with a manually resettable 5A fuse in order to limit the power output to what I considered a safe max for the 4AH battery. I use Anderson 30A connectors for the interconnection.
Item 3:
Homemade "Buck/Boost" converter based on 2 high power components from AliExpress built into an old PC power supply case.
The incoming battery power feeds into an adjustable "boost" circuit that I have set to produce 34v. This voltage is then fed into a "buck" circuit that drops the voltage back to 18.5v to match the laptop's spec.
The input stage accepts input voltages anywhere from 11v - 30v so this converter box can be supplied by 12v car battery, 18-20v powertool battery, 24v truck battery, or even directly by a solar panel with VOC of up to 30v max. (Supply needs to be capable of outputting approx 30W if laptop internal battery is already charged or missing, or 60W if the internal battery is low, and charging up while the laptop is running).
Item 4:
Just a hookup wire with Anderson connectors on one end and a standard 5.5 x 2.5mm connector such as you see on many laptop power supplies. (eg Toshiba supplies)
Item 5:
This DC connector takes the 2.5mm connector and adapts it to the special "3 conductor" Compaq input plug. The center pin of these connectors is designed for communication between the laptop and the OEM power supply it left the factory with. If the laptop communication matches the power supply communication then it enables proper charging of the internal laptop battery.
This particular adapter works with HP and Compaq - but not with Dell. Dell uses this communications pin to "read" what the power wattage of the power adapter is, and if there is no valid signal down this pin then the Dell battery will not charge at all. (Havent yet found an adapter capable of spoofing the comms signal on a Dell)
As well as relying on the BMS inside the Ozito battery I also have multiple fuses everywhere because I hate it when things get overloaded and the magic smoke leaks out of the electronic components 
