A lot has changed between Morrowind and Oblivion when it comes to the Battlemage and the Spellsword classes.

The Morrowind Battlemage:

Battlemages are wizard-warriors, trained in both lethal spellcasting and heavily armored combat. They sacrifice mobility and versatility for the ability to supplement melee and ranged attacks with elemental damage and summoned creatures.

• Specialization: Magic
• Attributes: http://elderscrolls.wikia.com/wiki/Intelligence_(Morrowind), http://elderscrolls.wikia.com/wiki/Strength_(Morrowind)

Major Skills:

• http://elderscrolls.wikia.com/wiki/Alteration_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Destruction_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Conjuration_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Axe_(Skill)
• http://elderscrolls.wikia.com/wiki/Heavy_Armor_(Morrowind)

Minor Skills:

• http://elderscrolls.wikia.com/wiki/Mysticism_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Long_Blade_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Marksman_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Enchant
• http://elderscrolls.wikia.com/wiki/Alchemy_(Morrowind)

The Morrowind Spellsword:

Spellswords are spellcasting specialists trained to support Imperial troops in skirmish and in battle. Veteran spellswords are prized as mercenaries, and well-suited for careers as adventurers and soldiers-of-fortune.

• Specialization: Magic
• Attributes: http://elderscrolls.wikia.com/wiki/Willpower_(Morrowind), http://elderscrolls.wikia.com/wiki/Endurance_(Morrowind)

Major Skills:

• http://elderscrolls.wikia.com/wiki/Block_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Restoration_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Long_Blade_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Destruction_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Alteration_(Morrowind)

Minor Skills:

• http://elderscrolls.wikia.com/wiki/Blunt_Weapon
• http://elderscrolls.wikia.com/wiki/Enchant
• http://elderscrolls.wikia.com/wiki/Alchemy_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Medium_Armor_(Morrowind)
• http://elderscrolls.wikia.com/wiki/Axe_(Skill)

The Oblivion Battlemage:

"Able to resolve most conflicts with either spell or sword. They are a deadly mix of scholar and soldier."

Specializationhttp://elderscrolls.wikia.com/wiki/Battlemage?action=edit§ion=2

• http://elderscrolls.wikia.com/wiki/Magic

Favored http://elderscrolls.wikia.com/wiki/Attributehttp://elderscrolls.wikia.com/wiki/Battlemage?action=edit§ion=3

• http://elderscrolls.wikia.com/wiki/Intelligence
• http://elderscrolls.wikia.com/wiki/Strength

http://elderscrolls.wikia.com/wiki/Skillhttp://elderscrolls.wikia.com/wiki/Battlemage?action=edit§ion=4

• http://elderscrolls.wikia.com/wiki/Alchemy
• http://elderscrolls.wikia.com/wiki/Alteration
• http://elderscrolls.wikia.com/wiki/Blade
• http://elderscrolls.wikia.com/wiki/Blunt
• http://elderscrolls.wikia.com/wiki/Conjuration
• http://elderscrolls.wikia.com/wiki/Destruction
• http://elderscrolls.wikia.com/wiki/Mysticism

The Oblivion Spellsword:

Specializationhttp://elderscrolls.wikia.com/wiki/Spellsword?action=edit§ion=7

• http://elderscrolls.wikia.com/wiki/Magic

Favored attributeshttp://elderscrolls.wikia.com/wiki/Spellsword?action=edit§ion=8

• http://elderscrolls.wikia.com/wiki/Endurance_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Willpower_(Oblivion)

Major skillshttp://elderscrolls.wikia.com/wiki/Spellsword?action=edit§ion=9

• http://elderscrolls.wikia.com/wiki/Alteration_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Illusion_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Blade
• http://elderscrolls.wikia.com/wiki/Destruction_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Heavy_Armor_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Restoration_(Oblivion)
• http://elderscrolls.wikia.com/wiki/Block_(Oblivion)

If you're confused, maybe it's worth debating on what fits a proper battlemage more and what fits a proper spellsword more.

Well, I'd say a Battlemage is a hybrid character who uses a weapon (and possibly armor) to supplement a mainly magical approach to combat, while a Spellsword is a hybrid character who uses magic to supplement a mainly warrior approach.

They lie on the same spectrum, but are different in what is their primary combat system.

I see the primary difference as mobility. The Battlemage is trained and equipped to fight in the line of battle with both magic and melee weapon. The Spellsword is trained to skirmish and support other troops in other roles, and can operate more independently if needed.

Battlemages belong to organised armies; spellsword are adventurers.

There hasn't been a consistent definition for the term "battlemage" for more than two games. In Arena, battlemages were more like mages who studied magic as means of combat and so they also trained in weaponry and light armour. Then there's cultural context, Both terms seem to be primarily of Imperial concepts. I've quoted something about that regarding spellswords below. As for the battlemages, there is or was the Nibenese battlemage aristocracy, the title of "Imperial Battlemage" and the Battlespire.The Art of War Magic written by a battlemage and it seems to be concerned with military tactics in general.

"Spellswords are spellcasting specialists trained to support Imperial troops in skirmish and in battle. Veteran spellswords are prized as mercenaries, and well-suited for careers as adventurers and soldiers-of-fortune." - Morrowind's description

If you mean lore and flavor-wise I think I can take a shot at this:

Battlemages are tacticians who study the art of war and science of magic. They don heavy armor, are well-learned scholars in battle-science and magical theory, and are extremely well respected in Imperial culture as warrior-nobles.

Spellswords are lightly armored skirmishers, mercenaries and sellswords who employ quick strikes with their weapons and devastating blows with their spells. I imagine most frontline altmer soldiers can be considered spellswords, as well as anyone who has a talent for magic and battle who wants to make some extra coin.

These are just suggestions, of course.

That's the way I always thought of them.

Its true that there's some overlap, especially regarding In-Game mechanics. In-universe, they do seem to be distinct on a career level and how they're regarded. Battlemages in Cyrodiil however are professionals and have earned the respect of such, no matter how http://www.uesp.net/wiki/Morrowind:Trebonius_Artorius they are at anything else. They have their own rank within the military hierarchy, and have a pretty long tradition of cultivating and maintaining those ranks in Cyrodiil.

Spell-Swords more or less seem to be a catch-all term referring to anyone who uses magic as well as the martial arts, and isn't generally regarded as a professional venture. That's not entirely true, as Morrowind's description of the class states, but finding people that say they're Spell-Swords would probably be rare, since most strike me as a more casual and varies wildly on a individual basis. Different cultures do have some practices with what we would call Spell-Swords, like the Nordic Witch-Warriors, the Ashlanders make use of melee and magical Skills, and the Thalmor soldiers seem to be mainly comprised of what we would call Spell-Swords.

If you ask me, I think the term "Spellsword" implies a warrior-mage that emphasizes the use of enchanted weapons (particularly swords) and heavy plate armor, since that would literally be placing the spell on the sword. Like the battlemage, a spellsword would probably still use spells (particularly in the schools of Destruction and Restoration) in addition to an enchanted blade.

Battlemages in the series have a tendency to appear more like standard mages in robes (often with armor) who seem to engage in combat and military strategy. Battlemages are also often depicted as preferring axes or staffs (the latter was Jagar Tharn's preferred weapon type) to swords.

Morrowind's and Oblivion's class selection suggests that there's generally a big difference in attitude between battlemages and spellswords, with the former being Strength and Intelligence based while the latter is Endurance and Willpower.

The fact that the classes changed from game to game suggests that even Bethesda is in the dark about this.

I'd offer an observation that might clear (or further cloud) the issue:

In Oblivion, there are actually two different "Battlemage" classes.

The player-character Battlemage is a Magic class, with Alchemy, Alteration, Blade, Blunt, Conjuration, Destruction, and Mysticism.

The NPC Battlemage is a Combat class, with Athletics, Blade, Block, Heavy Armor, Destruction, Restoration, and Sneak.

These are two very different "builds," so I suggest that the military form of "Battlemage" is more like the NPC version.

Ha, that was my conclusion as well

I think generally the commonly held approach makes sense to me if you were to look at their terminology. "Spellsword" suggests a general term for someone who uses magic and weapons, whilst "battlemage" suggests a person with similar skills employed militarily.

This probably sounds trivial to most, but frankly I wish they found another term for spellswords because I think it sounds too casual, and perhaps a little uninspired. I mean, I'm fine with Belrand being a spellsword, but not our august Champion/Dovahkiin...

Well, the Dovahkiin would be more of a voicesword, with the Thu'um and all that.

A battlemage is a mage backing up offensive magic with melee weapons, and not necessarily wearing armour.

A spellsword is a warrior wearing heavy armour and backing up melee weapons with offensive magic.

Except that in Morrowind a Spellsword had Medium Armor, and just as a minor skill. I don't think there's any consistency of armor type, for either class, from one Elder Scrolls game to another.

I think the fans put a lot more thought into these sorts of issues than Bethesda. I can see two Bethesda employees working on Oblivion and having a conversation like this:

Todd: Hey Bob, I noticed you gave Spellswords Heavy Armor as a major and Battlemages have no armor skill. Isn't that kind of opposite of what we did in Morrowind?

Bob: Yeah, so, what's your point?

Todd: Well, won't the fans notice? I mean shouldn't we be consistent with our lore from game to game? Or at least have a good reason for making a change?

Bob: Where's the fun in that? Consistency is the hobgoblin of a simple mind. Better to change it up now and then and give the fans something to debate on the forums. Just watch, they will still be debating why we made this change 9 or 10 years from now.

Todd: Good point, Bob! Keep up the good work!

To me a battlemage is more a "tank-mage" that hurls spells and bashes skulls with blunt weapons, preferably maces while taking hits in his heavy armor. I see the spellsword as a dude who imbues his weapons with spells, like a finesse fighter specialized in precision strikes clad in light/medium armor. I actually used a mod like that in oblivion for my spellsword: I would use my spells on my weapons, and their "charges" were actually drained from my mana pool. Good times.

Still, my point stands IMO - the Battlemage is a melee-capable mage, the spellsword is a magic-capable warrior

I've seen sorcerers (an armored mage) as more of the real "tank mages." Battlemages in my opinion wouldn't be able to tank as well as a sorcerer, but they would have greater physical combat experience with weapons, whereas most sorcerers would have nearly none.

Ultimately, I agree that battlemages (mage with some warrior abilities) tend to be more like heavily mage-oriented people who are also trained in combat to a smaller but still proficient extent, who also tend to be tacticians at higher levels, and at lower levels probably also would wear heavier armor. As someone mentioned in one of these topics in the past, the battlemage would be likely to blow a hole through a wall using magic, primarily use magic, and then use weapons or martial skills if an enemy gets too close or in situations that warrant it. They would be able to deal more magic damage and they would be able to take many hits (although not as many as a sorcerer), far more than a spell sword, however, the battlemage would be much less nimble and their lack of weapon strength/prowess would have to be supplemented by their superior magic.

As far as spellswords (a warrior with some mage abilities) are concerned, I've seen them as being primarily warriors who supplement their martial skills and acrobatic techniques with a spell or two. As someone mentioned previously as well, they would be likely to leap over a wall, rather than destroy it, and then quickly take out enemies one at a time, while using illusion or conjuration spells to distract enemies, and destruction spells if they just so happen to be at far range. They would specialize in lighter armor, would pack more of a physical punch, and be more quick and acrobatic than a battlemage, but they would probably be a bit of a glass cannon, in that they wouldn't be able to take much damage.

Basically, they're two sides of the same coin, IMO. If a battlemage and a spellsword were to fight eachother in purely melee combat, the spellsword would likely win almost everytime. However, if a battlemage and spellsword were to fight eachother using purely magic, the battlemage would win probably everytime. If both classes were to use both magic and physical combat, it would come down to who used their talents better.

The spellsword would want to focus on chipping away at the battlemage, overcoming their defenses, getting in close when they least expect it, and then attacking them at close range with physical strikes when they're weakened, while avoiding any offensive strikes with their acrobatic abilities. The battlemage would want to focus on using superior magic skills to cover as many weaknesses as possible, while anolyzing the spellsword for any mistakes they make if they try to get in too close, and then punishing them for their errors.

Ultimately, I think that a hardened battlemage in a combative scenario would have a bit of an advantage over a hardened spellsword, mainly due to the superior tanking abilities of the former, even with a lack of heavy armor. There's probably a reason why one of the highest magic positions in the empire was "imperial battlemage" and not "imperial spellsword." Although a lot of that, as some others mentioned, would be due to the battlemage's status as being more tactical, whereas a spellsword would be more of a mercenary or stand-alone operative.

Yes, and I agree. (I think that's essentially what I said in Post #2.)

and if I remember right in Daggerfall neither battlemage nor spellsword had an armor skill, but then I don't think Daggerfall had any armor skills anyways. Both had armor restrictions to what would be considered light armor either leather or chain. Biggest difference was in the primary skill set, battlemage had destruction magic plus two weapons skills whereas spellsword had three weapon skills with destruction assigned to major skills. Just goes to reinforce the battlemage is a melee capable mage, spellsword is a magic capable warrior line of thought.