Even if you remove the tool or battery, the charger will keep charging unless you unplug it or turn it off at the wall. The same goes for mobile phone, electric toothbrush and other gadget chargers.
Most things are sold in metric quantities these days, but if you're not happy working in metric, stick to imperial and convert it if you need to, or get the store to do it for you. The trick is to only work in one system to avoid confusion and mistakes.
It happens when warm air inside the room meets the cold windowpane and forms droplets of water. With double and secondary glazing, condensation can get between the panes, which isn't good for the window frames, especially if they're made of wood.
Flat roofs are another common cause because they're only watertight if properly sealed, and water tends to sit on them in a way it doesn't on pitched roofs. If you think your home has any of these problems, you could tackle them yourself, but it may be better - and safer - to get a builder or roofer in.