The basic LM2596 chip has internal thermal and current regulation,… according to the datasheet, and I suspect this is what is inside your potted regulator.
All you would need to add is something that allows for a trickle charge of the battery whilst allowing a modest supply drain for your Pi… But don’t forget some fuses,… think what your max current drain will be,… if your thinking just a Pi,… then a 5amp fuse should be plenty. And mount the fuse as close the the battery as possible,… as Lead Acid batteries has a tremendous amount of available power. (also use wire / cable rated at least fuse level x2 or more to ensure the wire does not become the fuse-able link)
To charge the 12v Lead acid battery you will need an 18v or 24volt supply as a fully charged Lead acid battery tops out at around 13.8volts,… and might hit 14v…
There are many charge type controllers around and basically they blip a pulse of power into the battery to keep it topped up…
Hope that helps…
My emonpi is in my server room (aka the cupboard under the stairs), along with a modem, router, PiHole and NAS. Because they’re all together they can all run on the same UPS, which is much more cost effective. I got an APC 850 (APC Back-UPS 850VA, 230V, USB Type-C and A charging ports, 8 BS 1363 outlets (2 surge) - BE850G2-UK | APC UK) which runs for an hour. You can get good deals on ebay if you’ve time to wait for them, my UPS was new and only £50!
A second consideration: the NAS and UPS manage each other - when UPS battery power gets low the NAS shuts down, and the UPS boots it up again when power returns. But I don’t have this relationship for the emonpi.
Thank you everyone for the comments on this thread, as this turned up at the right time for me and spurred me on to move forward with this.
Only last week I completely redesigned, relocated and re cabled all of my network infrastructure. One of the items I purchased was a PoE switch with the intention of using 2 ports to power my emonBase + RFM69Pi and an IoT hub via PoE splitters and then also look at a battery backup/UPS for the PoE switch.