--- Jim, if you'd leave a little of the message you're replying to at the top of your reply ("context") we'd all be able to see to whom you're replying without having to examine the header trail. Thanks.
Anyway, It depends on how your charger determines that the battery has been fully charged and puts it on trickle charge.
With the lock load on it it may determine that it _never_ gets fully charged and may just keep pumping current into it, along with the lock.
By using the charger in the way it was intended to be used and switching between the adapter and the battery when you get a mains failure, there will _never_ be any interaction between the lock and the charger, eliminating any problem that might crop up there. Besides, relays are cheap. :-)
-- John Fields Professional Circuit Designer