Guys I think it's got to do with age, if it's an early one like my D reg then you got to be careful and leave the bonnet open. But anything past that age like my previous E reg then it should be fine to disconnect and open it manually.
According to the manuals for the early and later Alps, the Lock/Unlock mechanisms are identical, the only thing to point out is the older the car, the mechanism behind the key lock is more likely to be very stiff or siezed.
Having just been out to recheck the operation, What I can say is that without the battery, they will lock/unlock with the key if the mechanism is in reasonable condition, however with the battery connected, there does appear to be a slight servo effect on the lock you are operating which is due to the central locking sending the pluse to the opposite lock, and as that pulse comes from the same contact on the relay, it is sent to both off and nearside doors, hence the servo effect on the door you are operating.
So if the lock you are operating is very stiff and cant operate the lock/unlock process with the battery disconnected, then by reconnecting the battery the slight servo effect might just be enough to overcome the stiffness, however this does not negate the basic fault, which if left is likely to get to a stage where even the servo effect will not overcome the stiffness.
I feel that once you get to the stage where the key by its self will not operate the mechanism eaisly and every time, it is time to do a bit of maintenance on the mechanism, if left it could get to a point where even with the servo effect, the key will not operate the lock, however it will still operate from the fob, as that is not directly connected to the stiff part of the lock.
Hope this all makes sense to you

1990 GTA Atmo, 2003 Jaguar X type 2.5SE Auto, 2018 Kia Picanto GT-Line-S 1.25