Dave Plowman (News) brought next idea :
Blurb with it suggests it's just a regulated 13.8v PS. Which should be OK
for the sort of charging use it would normally get.

Which is what I have and despite the assurances that 13.8v will not
damage batteries if left on permanently, having lost batteries before
due to evaporated electrolyte when left on....

My regime now is to leave the PSU on, but disconnect the battery after
a couple of days of non-use. I put it back on throughout storage, maybe
once a month for a couple of days. Sometimes I will put it on a proper
charger, just to bring it to a full charge. The battery is only there
for the mover and as a backup to the mains and the PSU.