A lot of emphasis on CTEK charger. These seem to be really quite expensive, is there a recommended model of this type or a more reasonably priced alternative?
Just make sure the charger of your choice is safe to use while the battery is connected to the car's electronics.
IIRC it shouldn't exceed a charging voltage of 14,5V!
You are right: CTEK-charger's are expensive - however, they have a track record of being very reliable.
(I have a CT5 Start-Stop charger myself and use it to occasionally recharge the Jazz's battery (more frequently during the cold season) and always, while the battery is fully connected.
So far - three years - and nothing bad to report.
Of course, there are other (modern!) chargers available at lower prices.
Just refrain from using an old transformer-based "clunker" on a modern car, while the battery is still installed!