Group Text gives noticable battery drain

[AMS1976]

I'm in a group conversation with 3 other friends.
On days when all 4 of us are texting to the group conversation at the same time, I can basically watch my battery meter dropping like a lead balloon.
On days when we aren't texting each other, the battery is completely normal (a battery life which, in general terms, I've been very happy with since upgrading to the S5).

I can be on YouTube, Twitter, taking photos, texting individual friends, etc, and I get typical and very reasonable battery life while doing multiple "heavy lifting" tasks on the phone. WiFi and/or cellular have no noticable effect. The phone has a great battery life outside of the group texting.
Then, when my friends and I start engaging the group text thread, the battery just plummets.

My battery details in Settings says Messaging accounts for 1% of the battery drain since the last time the phone was unplugged.
That % in Settings never reflects an unreasonable amount allocated to Messaging (i.e, it never says Messaging is the cause of 20 or 30% of the battery usage). But it's undeniable that a significant battery drain happens specifically when group texting.

Frustrating.