On Tue, 11 Aug 2015 02:33:14 GMT, Windmill wrote:

But the charging current you'd get from a north-facing window
would be
tiny. Did you measure it?

ISTR (badly) a few mA at 0.5 Hz or slower.

I don't follow. Where does a frequency of 0.5 Hz come into it?

The LED flashes, when on it takes most of the power from the panel,
off the battery gets it. The LED flashes as when on it pulls the
voltage below that required for the LED conduct so it stops this
means the voltage rises to the conduction point, repeat.

--
Cheers
Dave.