Hey Bojan, Batteries with an air system has got the possibility to recharge it even when it's not for 80% discharged. So when when the driver has got a lunch break for 1 hour it is possible to do so without damaging the battery.
Normally you can remove the air pump out of the charger but then some setting has to made which is in your case impossible so I would try to put a plug (with a very small hole ) into the hose of the air pump so the pump can work with some resistance on it.
As I wrote before you have 7 times to try and then the charger goose in safety!
Regards
Marcb