▲ a batch of...和this patch of...用作句子的主语时，谓语动词通常都是用单数。又如：

A batch of rolled steel was allocated to us.  调来一批钢材。《现代汉英综合大词典》

The first batch of cakes was burnt.  第一炉蛋糕烤焦了。《简明英汉词典》

Every day another batch of papers reaches the manager demanding his attention. 每天都有新的一批文件送交经理批阅。《朗文当代英语词典》

This batch of products is well made.  这批活儿做得好。《现代汉英综合大词典》

▲ 另外，章振邦《新编英语语法概要》中有如下说明（你的问题也属此类）：

如果主语是由“a portion of, a series of, a pile of, a panel of +名词”构成，不管名词类别为何，谓语动词通常用单数。例如：

A large portion of the products (大部分产品) is to be exported.

A series of accidents (一系列事故) has been reported lately.

A pile of logs (一堆木头) was set beside the hearth (炉边)。

A panel of distinguished people has been chosen to judge this competition. (已经选出由知名人士组成的专门小组来评判这次比赛。)