Reducing variable voltage to a lower variable voltage in a dc circuit
You have to use a regulator to power the Voltage Current meter.
There are many options and two of them which could strike my mind is using:  


Buck regulator such as LM2574  
Linear regulator with extended input range using FET and may be two in series in order to keep the dissipation low.  


Option 1 is simple.    

Set the output voltage to 20 V nominal and the display should be fine. Normally the power consumption of the volt-ammeter will be ~&lt;30 mA. So, load is not a concern. Then, you can hook up the input probes of the meter to the battery.  



Option 2
This is not complete solution but the hint to the design:
Instead of TPS79228 you can use 7805 regulator too, but care to be taken while choosing FET. Breakdown voltage has to be higher than 60 V . Power dissipation and gate voltage to have the load current of at least 40 mA are two second major concerns to be considered .

Reference: TI application note