What is this please?

I have just acquired a 2003 Vogue - TD6. Looking around under the bonnet today I came across and item that is wired in and is simply 'floating about' on top of the left side suspension strut adjacent to the battery. It has three LED's, only one of which flashes at any one time and the colour varies from red to yellow. Could someone please advise me what this might be. I'd be grateful.
I have attached photos.
Thank you.

Ctek Battery charger what's called the comfort lead. CTEK MXS 5.0 Car Battery Charger - the smartest battery chargers in the world!

I have them on all my cars. they are are about the best for keeping a battery tip-top

That ist brilliant. Thank you - I will seek one out.