The battery on my car has run down even though it's just been parked up - what's the cause?

The battery on my Opel Omega has run down even though it's just been parked up. What's the cause?

My car's start-stop won't work because of a partly discharged battery - would a trickle charger solve the issue?

My 18 month old Mercedes-Benz E-Class won't automatically stop-start anymore due to a partly discharged battery. It's left in my garage for weeks at a time, so it's understandable. I took it for a 120-mile...

My car's battery is discharging when it's shut down and stationery - any advice?

My Ford Mondeo's battery is discharging when it's shut down and stationery. It is a new battery, but the car is nine years old, with 53,000 miles on the clock. Any advice?