A more accurate etymology is: Bear-shirt (Old Norse: ber-, bear) + (Old Norse: serkr, shirt) i.e., shirt made from the pelt of a bear, which was the stereotypical berserker garb.
For the original take on berserkers, read the Vatnsdœla saga, Haraldskvæði and the Völsunga saga (in the original, if you can manage it).
A more accurate etymology is: Bear-shirt (Old Norse: ber-, bear) + (Old Norse: serkr, shirt) i.e., shirt made from the pelt of a bear, which was the stereotypical berserker garb.
For the original take on berserkers, read the Vatnsdœla saga, Haraldskvæði and the Völsunga saga (in the original, if you can manage it).