I would love to see that!
Cause I maintain all my battery sensor entities in separate groups anyway. Currently a manual job, can maybe be automated with some template magic on „identify all battery sensor entities of Aqara devices“.
Anyway, if the blueprint would support groups and expand them (so the rest is working as currently with a list of affected sensors in the notification etc.), that would save me from editing all blueprint based automations too in addition to the group change).
Sidenote: expanding groups to list the names of their entities in a certain state:
{{ expand('group.batterystate_lowlevel')|selectattr('state','eq','on')|map(attribute='name')|join(',') }}