XC6190 is a voltage detector (1.47v trigger voltage) with what it claims is just a 10na quiescent current. Sounds pretty good to me: https://www.mouser.com/datasheet/2/760/XC6190-837296.pdf

@Mishka Ah yes, that is true. In this case though I went out of my way to keep the PCB dimensions as small as possible so that someone could have it made at OSH-PARK for super cheap--just $0.30 per board. If I ever figure out how to post a complete set of KiCAD files, then I guess maybe then everyone can modify it to suit their circumstances. Until then, it will be hard to have one's cake and eat it too.

If you wish, you may substitute S-1313 ( http://datasheet.sii-ic.com/en/voltage_regulator/S1313_E.pdf) for the MAX8887EZK27 LDO

What is the max ampere capacity of 3.3V battery it can charge ? Is there any upper limit like 1000mAh or 3300mAh like that ?

Right you are. Live and learn (even at 81), and I even learned a new word -'vias.' Thanks.