Here's another approach that avoids look-arounds.

Win8 Strawberry 5.30.3.1 (64)  Thu 04/14/2022 15:59:05
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

use Data::Dump qw(dd);

my $rx_ab   = qr{ A \s* = \s* [BCDEFGH] }xms;
my $rx_stop = qr{ batch \s* = }xms;

my @strings = (
    'A = B foo A=C batch = bar A = D',
    'A = B foo A=C bar A =D',
    );

for my $s (@strings) {

    my @captures = $s =~ m{
        ($rx_ab) | $rx_stop (*COMMIT) (*FAIL)  # wrong order?  see upd
+ate below.
        }xmsg;

    dd \@captures;

    }

^Z
["A = B", "A=C"]
["A = B", "A=C", "A =D"]
[download]

You will have to elaborate the $rx_ab and $rx_stop regexes until they match what you want. I think the | The (*COMMIT) special backtracking control verb is available from Perl version 5.10 onward (update: and is non-experimental from version 5.20 on).

Update: Because of the way Perl ordered alternations work, it seems to me that the order of the alternation used above should be
    $rx_stop (*COMMIT) (*FAIL) | ($rx_ab)
This eliminates the possibility that the A pattern can accidentally match the 'batch' stop marker.