What's exactly is the problem with your car
@Accy cyclist.
Is your car failing to start on a regular basis due to the battery being discharged. If it is, take it to garage to check out whether the battery or alternator is knackered and then get sorted accordingly.
Or are you just worried that your car will let you down in your time of need. If this is the case and your happy the battery and alternator are in good order, buy a lithium jump pack or get some road side assistance package such as the RAC.
There's no point in worrying about your iron chariot letting you down somewhere. Sometimes we just have to put our faith in our cars and deal with the unexpected breakdowns when they happen, otherwise we would never go anywhere through lack of trust..
My car is an old banger held together with bale twine and cow muck and wouldn't bat an eye lid to going fat a field (restrictions permitted of course)
Life's way to short buddy to worry about a cars future reliability. If it starts and you're satisfied it's charging and the battery is not duff don't worry.
If you've got concerns let a garage take a look at it.
Short journeys will eventually run a battery down. The power it takes to crank engine will take a few good miles of driving to replenish it again. I would say at least 5 miles of driving is needed to replace the energy taken from starting. Letting a car ticking over to charge a battery isn't that effective to be honest as the engine is only ticking over and subsequently spinning the alternator slowly. When i start my old car the voltage displayed in the dash will show its pushing around 14.5v into the battery. After around 5 miles it settles to around 13 to 13.5v
I hope this helps Accy.