I’m using DJI prop guards that came with my combo package. Yesterday I received a response to my inquiry from another Spark Pilot informing me one option is to use a “O” ring which looks like a good solution.
The design change of the battery only fixed one (of several) causes of BES (Battery Ejection Syndrome) -- so there will continue to be mishaps.
Batteries will still fall out due to human error: a) if battery is incompletely locked and loaded the mechanism won't positively engage. b) if tabs/springs become weakened from rough battery removal technique they become less reliable.
I don't expect a cure for BES until we get a whole new Spark -- hopefully with a top-loading battery and a locking mechanism that has visual confirmation of engagement.