ChargeInhibit Assertion in pmset

I'm in trouble with the AC plugs on the train I use to go to work they're intended for charging mobile phones or small devices, so when I plug my mac because the battery is flat after 2min the power is cut off, so i'm trying to inhibit my MBP battery from charging when plugged in. I found that in older versions of OSX the pmset command included the parameter ChargeInhibit, which in Yosemite is not longer implemented.

Tried using this piece of code but does not work.. http://stackoverflow.com/questions/7670158/creating-a-chargeinhibit-assertion-o s-x-10-6-8

Any suggestion?

Thanks