Need assistance folks..

I have a 12v solar charger from Maplins, got few years ago. I need anyone that has one to check the polarity at the terminals.

When I installed in the shed, I had to disconnect and reconnect the terminal wires. I connected +ve voltage to the red terminal and -ve to black terminal, so metered positive on red and negative on black. All clear so far!

Thing is I have a halfords mains charger, and checked the terminals on it lately, and it reads -ve on the red and +ve on the black. I assume this is to generate a current within the battery while charging.

I never really used the solar charger much so I don’t know if it was charging or draining the battery but now I want to use it more and make sure the terminals are connected correctly.

Thanks for help.