I am generally satisfied with the 40 Ah one. Theoretically, a 45 Ah battery can be used for 10 hours.
The unit of battery capacity is the ampere-hour (AH), i.e. ampere-hour. Battery capacity multiplied by battery voltage equals the theoretical electrical power the battery can provide. For example, a 40 amp hour/12 volt battery can provide 480 watts of power for one hour. But this cannot be achieved in practice