I have the basics down, solar panel charges the batteries, batteries power the LEDs switched by a PNP transistor. But... I really want to be able to test how long it will last and how much power I need to gather from the solar cell/s to provided adequate illumination time.

Commence testing:

I have the batteries powering the LEDs and the UNO + Ethernet shield combo is sucking in voltage data and saving it to a CSV file on the micro SD Card. It has been running for +18 hours so hopefully that should give me enough data to look at the voltage over time, which will help me look at a discharge curve but also the current used.

I will update once the batteries drop to 2.5v which is where I think the LEDs will be too dim to be useful. I reckon they have another day left.

The next test will be of battery charging but that will have to wait until it is not raining, I know it will be waterproof but I am not.