You mean Fibrefoam the brand or just foam battens in general? Some of the early foam battens were very brittle even new. One of the USA manufactured brands supplied as standard equipment by one of the large manufacturers used to break on hitting the water even in a mild capsize.
I've used Fibrefoams for 20+ years and can only recall one or maybe two breaking in that time. A lot depends on how any batten is stored over that many years. Sun and heat are the enemy - as they are for the sail. Also battens won't survive if bent around 90 degrees with force, although that seems less likely with your top battens breaking.

Cheers