Normally it would be more productive to steal the whole bike.
Taking a battery off of a bike makes it far less desirable to steal the bike so that would be one of my main motivations for removing it.
It is a realistic question, batteries are not cheap. If a seat or front wheel can get stolen so can a battery.
I don't recall anyone saying someone is fear mongering because they say they have to buy a better lock or take their front wheel with them.
Would I take my 10lb battery off and haul it around with me while I site see? Heck no, I think my lock mechanism and housing is good. Would I bring it into the house or into work. Yes.
sorry if this is no longer pertinent, but batteries get grabbed all the time in amsterdam. a lot of batteries just reuse the same locks on their cases and you can order the keys off ebay/aliexpress, so people will definitely nab them. haven't seen anyone break the mounting plate to try to get to one, i think common sense says that it's a bit stupid to steal a battery if you're going to risk destroying it with a pry bar in the process. also it may be worth mentioning that this mostly seems to happen to premade bikes (rad, super73, etc.) since those batteries are very expensive and easy to resell to people who need spares. i have friends who have PVC style batteries that aren't even locked to anything just chilling in a crate on their bike and they don't get stolen. if the bike looks shitty enough people tend to leave it alone.
now i live about a 25 minute train ride outside of amsterdam and i don't really see/hear of this happening. so unless you live in like new york or LA or something then you are probably fine. when i lived in austin i had headlights, grips, mudguards, crates, etc. stolen but never a battery.