Lunar Solar?

Ued saloon light as nearest 12volt light for test.

Poblem with 12volt electrics. Does the following sound like a knackered battery.?
Put it on charge all day, site cable on mains in house, needle went over to far side of greeen indactor strip on dial. Turned off charger and needle went back over to red. Turned on the saloon light nothing. Switched charger back on. light worked.
With charger still on, no matter what position the car/caravan light is in 12v saloon light still came on, so assume it bypasses this switch when not connect to a car or that's only used when towing.
I could take battery out and charge it in my garage but thought first it might be something else. Battery is around 4yrs old. All six 12v fuses on control panel checked and are ok. Oh! multimeter test at 20 settting DC gave reading 2.5 if I was using it properly.
Many thanks in anticipation.