Light meter Sverdlovsk-4 (экспонометр Свердловск-4) battery case

This is the first version with two batteries. First, this light meter was pack with tiny battery for 3.75 volt and 0.25 Ah. But on the back of a light meter was written: possible currency: 3-4 volt. Now, when i use two AA acumulator battaries i have only 2.75 volts. But it still works. But i am not sure about accuracy of it measurement. So, nest version i want to use dc-dc step up converter to give 3.7 volt.

Fusion 360 source file included, so you are welcome to improve this