You can use a micropower regulator such as http://uk.farnell.com/microchip/mcp1702-3302e-to/ic-v-reg-ldo-250ma-to-92-3/dp/1331485, which has only 2uA quiescent current. I use the 5V version to power the mcu in designs that run from a 9V battery and have no on/off switch.
Given that most 4v2 batteries have built-in over and under-volt protection,
As I understand it, the PCD8544 is the controller, not the display. As far as I know, the display itself is rated at 3.3v.
QuoteGiven that most 4v2 batteries have built-in over and under-volt protection,I would never make that assumption or statement. Only by verification of the specific batteries datasheet can one tell what if any internal protection it offers. Buyer beware. Many Li-Po cells have no such internal circuitry added and rely on it being provided external to the cell.Lefty
The two outside ones look as if they have the resistors for the LEDs. The middle ones, well I can't see them, my guess is that you'd have to add an LED limiting resistor for that one. Maybe they are top-side though. Which one did you get?