or, if you want a list-of-lists:
k = 11;
bank_tags = {};
bank_pcs = {"BGB1BESS001_B" || bank || "_W", "BGB1BESS001_B" || bank || "_A", "BGB1BESS001_V" || bank || "_W"};
For( i = 1, i <= 6, i++,
bank_num = 6 * (k - 1) + i;
bank = Char( bank_num, 10, 0 );
bank_tags_i = Eval List( bank_pcs );
bank_tags[1 + N Items( bank_tags )] = bank_tags_i;
);
Show( bank_tags );
/*{{"BGB1BESS001_B61_W", "BGB1BESS001_B61_A", "BGB1BESS001_V61_W"},
{"BGB1BESS001_B62_W", "BGB1BESS001_B62_A", "BGB1BESS001_V62_W"},
{"BGB1BESS001_B63_W", "BGB1BESS001_B63_A", "BGB1BESS001_V63_W"},
{"BGB1BESS001_B64_W", "BGB1BESS001_B64_A", "BGB1BESS001_V64_W"},
{"BGB1BESS001_B65_W", "BGB1BESS001_B65_A", "BGB1BESS001_V65_W"},
{"BGB1BESS001_B66_W", "BGB1BESS001_B66_A", "BGB1BESS001_V66_W"}}*/
If you want a string rather than a list, try @vince_faller answer with Concat Items( bank_tags, "," ) to get the list items in a string with commas.
Craige