I’m keeping mine topped up for free while it’s not being used...

 

Here is an interesting video about how you can monitor the state of your 12 Volt battery from an "App" on your phone..
It also answers the question :-
"Is the 12 Volt battery on the ZS EV also collecting a charge, when the the traction battery is getting a charged from either the Granny or the Wall Box".

I've been using similar trackers to these for some time, they're very handy for cars you don't use every day. Frankly it even alerted me to the car I do use every day having a failing battery before I got stranded, so yes they are great. Wish the manufacturers would allow reporting on the battery condition via the apps this way, they have the capability in most modern cars.

Though I have to say I think the particular battery state tracker he's using is very dumb. It appears to be using the output voltage as a direct linear report of the battery capacity %. In reality this is a huge over simplification. The better ones will measure the capacity of the battery by measuring capacitance or resistance as well as straightforward voltage, and they'll give a better indication of charge % even when the battery is under heavy load and the voltage is sagging.

 

Anything is better than nothing I guess ?.

 

False positives aside, yes...

To be fair it's much less of a big deal if the 12v battery in an EV is a bit low. It's not like it has to pump out a 200 amp current to turn over a cold V8 block flooded with tar-like oil to get itself back up and charged. It just has to trip a few relays and there you go .. a nice warming flood of electrons from the DC-DC converter after you've turned the HV pack on ..