Dear Bartosz,

Thanks for your reply.
that's right! the solar circuit need a voltage regulator.
Indeed, I prefer the seiko's small package CMOS voltage regulator -- S-817 series.
features:
max. Vin = 10V
Vout = 1.5V
It would prevent from the battery overcharging problems, but it still cannot help for the power up reset. (situation when someone place it under a lamp but cannot power-up.) Any more suggestion?

Do you talk about the low drop out voltage regulator or the DC-DC converter?
I found this link but it seems not suitable for watch model. (bulky & draw large current)
http://www.maxim-ic.com/appnotes....number/364
Watch don't expect to reset overlight

Hence, I have tried the solar cell direct under the Sun at 3 separate-day, which have a I-op for ~4.8mA. And the final watch product have a plastic mask which block 2/3 intensity.
The I-op become 1.88mA after I place the plastic mask.
In a cloudy day, the I-op = 0.7~0.8mA (with plastic cap)