I use one of these maintenance chargers on my little used vehicles :-

https://www.amazon.de/NOCO-present-automatic-intelligent-batteries/dp/B0828K688S/ref=sr_1_4_sspa?crid=17XSR28SMCEPJ&keywords=genius+charger+2A&qid=1692139515&sprefix=genius+charger+2%2Caps%2C209&sr=8-4-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1