As this is specific to each laptop you would check the Voltage output of your power brick then build the power pack to match. For the power to the laptop connection, scavenge one from a dead charger.
http://lifehacker.com/5898653/hack-together-your-own-external-laptop-battery-pack-for-60 for example but that's missing a fuse and has poor soldering techniques.
Only one comes up for that search on google. and it will not let me copy the title. So is there any other ones?
Lenovo store is showing nothing.
If I knew what plug to use and what voltage I could build one my self. out of 18650 cells
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