It's not about "getting away" with anything it's about designing the system correctly and measuring/calculating your system current.
To make this clearer, the modes on Texecom bells:-
SCB - only draws charging current from panel, activation current from bell only.
LC - divides the activation current between the system and the sounder battery where possible, still a little quieter than SAB
SAB - the standard full volume option, where activation current is always drawn from the system and sounder battery is only for hold-off.
We are talking hundreds of mA difference between the options, from about as much as a passive, to about half an amp.
Personally I would suggest you connect one to the panel whatever you do, then at least one should operate correctly even if you get the programming or settings wrong.
But it's all down to the system design and where your powering everything else from.