I want to feed HD44780 LCD module with battery power. I use AVR controller (like ATTiny24L) and I want to make a compact device so AA batteries are too big. 3V flat battery is small enough and can feed controller but LCD wants 5V. So the question is: is there any sence in transforming 3V to 5V? Or battery life will be too short? Also if there is sence what is the right way to do it?
You can easily make a 3V to 5V converter but if you are not used to this it can take more effort than the project you are trying to power.
You can get about 80%+ efficiency from a typical 3V to 5V converter.
IF 5 x AAA is acceptable then with a linear regulator you get about 85% energy efficiency across most of the battery range. You can also get small premade stacks of NimH cells made for cordless phones etc. 5 is less usual but probably available. These are easily recharged with a simple resistor and zener arrangement if charge time is unimportant.