The reason why batteries fail if they’re not used, or they’re only used for stop-start or short journeys, is that they don’t get the chance to recharge properly.
The technical explanation is that this 'under charging' leads to 'sulphation' if the battery voltage is allowed to remain below 12.4 volts. Sulphation is the hardening of the lead plates within the battery and it reduces the battery's ability to accept or hold a charge.
If you do only use your car occasionally and for short journeys it's worth investing in an intelligent charger/battery conditioner. This can be left connected for long periods without risk of damage to the battery.
Alternatively, you could get a solar charger.