There is a historical record of the battle with 50 thousand to 0 score.
According to Procopius, during the war with Vandals, there was a battle near the
Bourgaon (Libya) in which the Roman general Solomon defeated the army of Moors.
And there perished in this struggle, among the Moors fifty thousand,
as was declared by those of them who survived, but ...
Salsu River in 612 is a strong contender, made all the more notable by the victor's forces having been massively outnumbered.
In the course of the Second Goguryeo-Sui War, a 300,000-or-so-strong Sui army attacked approximately 10,000 Goguryeo cavalry at the Salsu River and were almost completely destroyed, with only 2,700 (less than 1% of the original force)...
https://en.wikipedia.org/wiki/Battle_of_Cajamarca, assuming that contemporary accounts were accurate.
Conquistador Francisco Pizarro ambushed the Emperor Atahualpa. The Spanish suffered no deaths and one wounded. The Incans suffered 2000 dead with 5000 more taken prisoner.
This castle was defended by a force of 30 (I found a number of references that state 28) against an attacking force of both the Welsh and French with siege engines and battering rams. (1403) It's even mentioned on the netflix series "Secrets of Great British Castles".
I don't think it's known exactly the ...
The battle of Aquae Sextiae (102BC)
As with all ancient battles there is a wide variety of figures thrown out for the casualties and participants for this battle.
Roman Total Forces = 40-50k (6 Legions plus auxiliaries) &
Roman Casualties = 500-1000
Teutones/Ambrones Total Force = 50k - 150k &
Tuetones/Ambrones Casualties = 30k - 120k
The Battle of Agincourt (1415)
French strength: 12,000 - 36,000 (modern estimates)
English strength: 6,000 - 9,000
French casualties: approx. 6000 killed
English casualties: 112 - 600 killed
Strength ratio (F:E): min 4:3, max 6:1
Casualty ratio (F:E): min 10:1, max 53:1
Numbers above from Wikipedia entry
History.com entry which ...
Another colonial battle: Battle of Namutoni (1904) in German South West Africa (today's Namibia):
Four German colonial soldiers (Schutztruppe) and three German reservists defended the Fort Namutoni with 1500 rounds of ammunition against about 500 Ovambo warriors. The Germans held out all day and retreated during the night without casualties, the attacking ...
Pearl Harbor attack:
Discarding the materiel lost, the USA had 2,335 killed and 1,143 wounded, while Japan had only 64 killed and 1 prisoner. That makes a ratio of 1:56.
If one adds in the materiel probably the difference is quite bigger.
Battle of Sidi Barrani:
During operation Compass, the British had 624 losses, while Italy had 2,194 killed, 2,286 ...
1988 - Battle of Afabet
Fought between an Eritrean People's Liberation Front (EPLF) force of around 15,000 and an Ethiopian army numbering 20 to 25,000, this was a huge defeat for the latter.
Ethiopian casualties were over 18,000 killed or captured while EPLF casualties amounted to only 394 (125 killed, 269 wounded, giving a ratio of at least 45 to 1.
Battle of Gaugamela in 331 BC between Alexander and Darius III's Persians.
One of Alexande's great victories. Even if we take the highest estimate for Alexander's casualties (1,500) and the lowest for Darius III's army (40,000), it still gives a ratio of 26.67 to 1.
Battle of Carrhae in 53 BC between the Romans and the Parthians.
This is the famous battle ...
It's actually quite difficult to point to a specific answer because, as your Boudica example shows, in many cases casualty estimates are not very reliable. The 80,000 figure given for Boudica's forces is considered to be a rhetorical device and not an actual factual number - a problem that plagues many pre-modern accounts.
Another difficulty is measuring ...
Tsushima 1905. 117 vs 4380 dead. Fleet engagement, so the Japanese + Russian numbers of men, combined, probably were over your 10k threshold, but that 4380 looks like it was most of Russian fleet.
The Invicible Armada lost 15000 men in 1588, but most of that was also due to weather on the retreat trip around Scotland. English losses were about 400. The ...