Solar Panel Shield, 3.7v battery - only seeing red charge LED?

Hi everyone,
new to the forum and hoping this is the right place.

Building a project for my MSc dissertation, and for some reason the shield is only charging (or at least, showing a state of charge).

I’ve checked the battery voltage, it’s 3.7v. I’ve had it in the sun for absolute days with my 138x160 panel and now have it connected to a USB just to see if that will change its state. With a brand new battery, am I missing something?

The Seeed Solar Panel Shield Wiki Page tells me the battery is just low and not charging. But with days in the sun, do I have to drain the battery down for there to be any trigger or something.

Thanks guys!

So, to my surprise the LED has now gone green due to being connected to the USB for a few hours.

Would this mean then, that the amount of power was not sufficient for long enough to top up or push the battery to it’s final charging position.

As the panel was in the window for absolute days, I do find it strange it took so long with no change, whereas the USB finished it in a few hours.