Edit addition on Multi Day Battles:
Good question. I've been thinking about it more as well. Its a rather poor argument from Runnells to begin with. He has a very poor grasp of battle, including how they are defined and their length measured. He seems to think that battles just can't last very long, but a very short amount of research found many multi day battles. There are various reasons for this including partial sieges, stand offs between armies vying for position, pre and during battle maneuver, and chasing down defeated armies.
He attacks the Jaredite account for having battles that lasted all day for multiple days, but there are plenty of ancient accounts that record similar or multi day battles. The Battle of Fei River and Hulao Pass both had significant stand offs. This is where the armies skirmished a bit, but they both held defensive positions and were trying to see how they could break the opponents position. In the case of Fei River Fu Rong moved his soldiers which precipitated confusion, panic and retreat. The opposing soldiers read the signs in the ground and then pursued them and killed 70-80% of the army (which goes to large numbers of casualties as well.)
The Battle of Red Cliffs also featured a long pursuit through marshes and difficult terrain which might be considered a multi day battle.
The Battle of Hulao pass Li Shimin (ruling name Tang Taizong), made the opposing army hold their position for hours which made them avoid lunch and get stiff, both literally and in their tactical responses. He sent a cavalry force to see how the enemy reacted. When they were slow in responding and reacted fearfully Li Shimin sent a full attack. The pre battle maneuver, stand off, then resulting attack and chasing down the fleeing army and regrouping remnants took more than one day.
In the Sicilian Expedition the Athenian army tried to besiege Syracuse. But the Spartans landed an army in reinforcements and they fought a series of engagements and built counter reinforcements. This shows how classifying battles and determining their length can get confusing (especially when people deliberately apply a narrow definition to prove something doesn't fit with "science"). But they fought a bunch of mini battles, including one at night where one side painted themselves white to better facilitate command and control, and the cumulative total was a spring and summer of near constant fighting. One could almost say that they would "fight all day and conquer not." (Ether 15:15)
In the Battle of Gergovia Caesar fought Vercingetorix. The latter had a commanding defensive position so the former had to rely on a combination of maneuver, siege, fighting, and desperate battle to finally break the Gallic army. Again, its tough to time the individual actions as each element of the campaign (active battle, siege, maneuver, marching), blended into each other. Thats why Runnell's complaint is so odd and poorly stated.
Which is really what you get for relying on reddit when you make sweeping pronouncements on military history. Thats why I went back to the basics in discussing how societies sustain war. The more complex they are, the more they can raise armies and sustain them in the field, which means they can fight multiple campaigns and many battles. There were some tribes such as the Cree who for much of their history were hunter gatherers that fought very few of what we would call battles, most were skirmishes with a few soldiers. But others like the Aztecs raised large armies, sent them on long campaigns, and had battle after battle on those campaigns.
The Jaredites had a sophisticated society, as seen by places like La Venta and San Lorenzo, with large populations that could raise and support large armies. Those armies could then fight a series of engagements: some combinations of pre battle maneuver (Ether 15:8), stand offs (even exchanging messages Ether 15:18), chasing down fleeing armies (Ether 15:10), and then finally it seems they were two punch drunk fighters with nothing left in their armies to maneuver or negotiate and they just came to a place, likely with ritual importance (15:11) and strategic value. In fact, their four year stand off while they gathered strength reminded me of the build up to the Battle of Hulao. They didn't have the logistical strength to go any further, so they fought the pivotal battle (that with the army marching, then standoff, and then battle, then mopping up it all likely took longer than one day) all happened at one place.
Hope this helps. Runnells just really doesn't know what he is talking about in military history.