Another Battery Question

[K3NJW]

This time about charge, or lack of it. I use my car every day, but the drive to work is only 5 or 6 miles, obviously with the lights on, the windscreen wipers and the heater (interesting use of the word). Having started to use the alarm/immobilisor option whilst the car is stood the battery ended up dead flat on Saturday.

Given the usage, and I assume the heavy drain on starting, how long does the average recharge last. I must admit I'm now going to get a trickle charge thing from Leven, I can't afford for it to go flat late at night with my wife in high heels ....... doesn't bear thinking about.