Maximum forward current on ESD diodes
Have you got a spare IO pin? 

If you have then get rid of the op-amp, make the resistor divider much lower impedance (suitable for a direct drive to the micro's ADC) and "connect" the potential divider to the 8.4V supply using a P channel MOSFET controlled by the spare IO pin via an NPN transistor: -



1 msec later you have measured your battery voltage and, given that you probably don't need to measure it for another minute or so, your average current is 1/60,000 times the current taken for that milli second when you connected the potential divider to the battery supply.

It's probably a good idea to have maybe 100 nF across the lower resistor too. You might also be interested in the answers provided in this stack exchange question. You might find that you can actually have very high impedance resistors directly feeding the ADC pin providing you have a capacitor across the lower resistor (see Hanno's answer).