As size 11 has a battery it is generally better to have a battery connected across the chargers terminals it "smoothes" the supply. Lights may be seen to flicker if there is no battery in the circuit. A battery at the end of its life is entirely suitable for this as would be a much smaller lead acid battery like a motorcycle battery. If the battery were physically breaking down there may be faults that would make it unsuitable.
Should you ever think of buying a new battery at some point one of the problems with batteries is because of the chargers that tend to be fitted to caravans and trailer tents. N.B. I HAVE NO DIRECT EXPERIENCE OF THE CHARGING UNITS FITTED BY DANDY THIS IS A GENERAL STATEMENT. So in general the type of units fitted by manufacturers TP2, Sig etc only charge with a maximum of 13.8 volts. I think the manufacturers were fixated at the possible risks of the batteries gassing. That is them giving off Oxygen and Hydrogen and the possible catastrophic result of this igniting. It matters not if there is a vent nor if the battery box is external to the camper. The thought of an ignition of this gas seems to be the limiting factor. Unfortunately this makes the units a bit naff for charging batteries. The charging takes ages and batteries arent ever "properly" charged. If a battery has come back from a weekend partially discharged it's much better to couple it up to an external charger rather than use the device fitted. They sort of work if you are permanently on EHU but that begs the question why have a battery?
The tech reasons behind charging isn't a three minute explanation and it starts to go beyond my understanding, navver and Peridot being better able to explain if you have complex questions. General battery buying advice [You must be registered and logged in to see this link.]
from someone who designs battery chargers for boats. These are far more gas sealed than campers but his chargers work at above 13.8 volts though you can't afford one and don't need it anyway.