Volt meter for Powerwheels

As many of us dads strive to be the cool dad and improve our kid's toys, we find that many many toys are in need of upgrades. My son wanted real headlights, a horn and a trailer for his F150 Powerwheels toy. I made the modifications and installed a dual battery power supply. The new setup lasts longer and fades slower than the stock set up but I was still always wondering how much was left on the batteries when out playing. Will we make it back without taxing the batteries at a low charge?

I looked at the dash and made up my mind that it needed a voltage readout. I ordered some tiny digital displays and picked up a momentary on switch from the auto parts store. Finding that the fake satnav was not going to work out to house my components, I drafted up a better fitting, stronger module that would also house the electronics securely while utilizing the original screws and mounting system on the back of the dash.

Simple loop circuit from positive to negative with a switch to keep it