Boost battery voltage by 150mV
When charging a battery I want it to turn off before it charges to the
  chargers full voltage.


Well, that's one way but it's likely you haven't considered an alternative idea of limiting the voltage to 4.1 volts.

Build a precision voltage shunt circuit that limits the terminal voltage across the battery to 4.1 volts. In simple terms this is just a zener diode but, it probably needs to have better accuracy (possibly 1%) and a much sharper knee voltage. In case you don't know what knee voltage is: -



Given that your terminal voltage appears to be that of a lithium cell, it's likely that at circa 4.1 volts the charging current will be fairly low and capable of being handled by the "zener circuit" without too much heat-sinking.