OK I'll consider an infinite input resistance voltmeter but it must have some input capacitance due to the insulation between + & - conductors must be non-zero capacitance.

 **So what do voltmeters measure?**   
Volts, of course with the potential to do work and conduct current but not until it is buffered by this zero-input current amplifier.

So there must be a charge transfer to the input of x pF. This equalization depends on the source having enough stored energy to transfer.  It doesn't have to be a voltage source of 0 Ohm impedance. It just must not be affected by the energy dump to charge up this voltmeter  $$ E=½CV²$$    

 let C be really small value in the voltmeter =\$1pF=10^{-12}F\$

All batteries are like UltraCapacitors with an intrinsic chemical cell voltage as the minimum.  The Li-Ion cell is about \$10kF=10^4F\$  

A drop of water between 1mm electrodes might be 100pF,  as the dielectric constant =80 relative to air.  Yet the battery will not notice the capacitance charge transfer to the voltmeter, but a charged drop of water might notice that load of 1pf.  However, keeping the voltmeter attached might be sensible if the capacitance ratio was known and corrected in any resulting acquired voltage.