Just to throw in another factor, the battery bank has a label(s) stating a figure (440 amp.hr).
Even if new, fully charged at this time of year they it will not be a 440 amp.hr bank. it will only be that if new, fully charged and the battery bank is at 25°C.
Even new ones will possibly not be that, as per Trojan threads
Check specification of batteries.
Having said that, I can only agree with other posts, if there is not a current leakage, lack of charging is very likely the problem.
Batteries can be knackered in days, let alone weeks if not charged correctly.