12 volt solar panel and 9 volt battery

Projects General Guidance
1

I'm planning to power an arduino using a 12 volt 100 mA solar panel http://cgi.ebay.com/1-5-Watt-W-12V-100-MA-SOLAR-PANEL-Grid-Tie-Inverter-/360367675971?pt=LH_DefaultDomain_0&hash=item53e7965a43
using the schematic found here: http://www.instructables.com/id/Self-Sufficient-Arduino-Board/
which will charge a 9 volt battery and power the arduino.

One of the comments on the instructables page said the following:
The solar cell amps should be max 20mA for a 9V battery - any higher risks overcharging the battery. In general terms keep the charge current under 0.1C where C is the amp hour capacity of the battery (9V rechargeables are usually round 250mAH).

The solar panel I was looking at was 100 mA. If I'm running the Arduino non-stop will over-charging of the battery be a concern?

2

If I'm running the Arduino non-stop will over-charging of the battery be a concern?

Depends on what is connected to/powered by the Arduino. If that (unspecified) stuff draws more than 100mA, then, no the battery won't be (over)charged.

If it draws less than 100mA, the battery will be charged. Whether it is overcharged, or not, depends on how much under 100mA the stuff draws.

3

You may want to consider hacking a solar setup that already has batterys.