The Gaming Den

How does the Battle Caster feat work with the "Ignore Arcane Spell Failure" abilities of things like the Spellsword? The ability pretty clearly qualifies for it, but there's nothing about how that would work.

Basically, it doesn't. The example clearly shows that it only applies only to spells from classes that let you ignore arcane failure from specific armor types (like light armor).

Then check this section out:
"This ability does not apply to shields, nor does it apply to spells gained from spellcasting classes other than the class that provides the ability to cast arcane spells in armor."

Since Spellsword does not grant spells (just adds spellcasting levels to another class that does), it does not get the effect of this feat.

Basically, this feat is meant for Bards, Assasins, Hexblades, Warmages, Spellthieves, and Warlocks, as well as some PrCs that grant a little arcane casting.

So apply the same reasoning to the Suel Arcanamach which both gives spells and an ignore spell failure chance by percentage rather than "armor weight".

"This ability does not apply to shields, nor does it apply to spells gained from spellcasting classes other than the class that provides the ability to cast arcane spells in armor."

The bolded section says that it does not apply to your Wizard spells if you qualify for the feat out of Bard. It doesn't say anything at all about prestige classes that are not themselves spellcasting classes.

Of course, I don't actually know what Battle Caster says it does, so that's all the interpretation I can do.

-Username17