We just returned from a 2-night dry camping trip. Since it was only 2 nights I decided to go with our puny group 24 battery that came with the 1575 (we rarely use it and instead use a group 29 battery almost always).
The group 24 (from our dealer) came with a crappy (group 24) battery box that is square.
I wasn't sure if the battery lock would work with this box, but it did (a loose fit, but secure "enough") so I took a couple of pictures.
You can also see that the 2 battery cables & the Victron Battery Monitor wire aren't in the way of the lock either.