My old Corolla is on its last legs (or wheels) but I want to keep it running until Christmas at least.

Mechanically, it's not too bad, but the battery is quite duff. It'll still start the car - just - as long as I run the engine every day.

But I was wondering if I can slightly increase its lifespan, maybe by adding distilled water?

Only thing is, it's one of those batteries that has a little window (which shows nothing, not even black) so I wondered if I were to drill a hole in the window, I might be able to add water.

Ideas please.