Make sure you install the CR1220 coin cell battery, the RTC chip needs it even if you don't use the battery backup.
As long as the clock is plugged in, the backup battery isn't used. When unplugged, the clock should keep time for many years - 20mAh / 500nA = 4.5 years
We use a high-efficiency white LED backlight display so the whole clock only uses about 50mA at 5V! Likewise, the power supply we provide is a nice switching supply, which means it runs at 80% efficiency or higher! So total power usage for the clock is under a half Watt.
How much energy does this clock require to run?
Check out this detailed tutorial
The MONOCHRON is designed to use a KS0108 LCD, these are monochrome displays that are very very well documented and understood. They're very popular for hobbyist use.
The clock is designed to control a monochrom KS0108 display. Note that these displays come in two 'flavors' of pinouts, you'll want one that is equivalent to our stock KS0108 LCD. So you can plug in any KS0108 display with the same pinout and it will Just Work.
It's possible to use a different kind of display like a SED1330 but note that it won't just work, you'll need to write some code and possibly rewire it!
MONOCHRON® is a registered trademark of Adafruit Industries