@NeverDie Use additional battery is an interesting idea. My only concern is that the harvester IC will drain it if connected to input. On the other hand it looks like the IC will work just fine as long the STORE has some voltage. And the STORE is connected to battery, which is charged by the harvester IC - i.e. the rechargeable battery is exactly the battery used to prevent IC from shutting down. But perhaps I missed something - still have no boards for test. Regarding solar cells from a calculator - yeah, that was my first intent, but have no solar calculator out there. Taking in account that such a calculator costs three times less than this SolarBIT thing I have no excuse for not to buy one from a local store - going to fix that tomorrow

I tested the Version 11 design, and it works. Therefore, I'm removing the "work in progress" moniker.

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.