I've seen this distinction elsewhere, so it's not something TDI_Power made up or even members of this forum made up. VAG makes neither batteries nor Oil Filters. They contract that stuff out, hence the OE/OEM differentiation. When the OEM sells to VAG to sell to you, it's branded VAG and is an OE part. When the OEM sells directly to you, it's branded by the OEM.
Right. But what's important is that Hengst makes the OE equipment for VAG under contract. So when you buy a Hengst branded filter, it's made by the Original Equipment Manufacturer (though it might be made to slightly different specs than VAG required for their order). Generally, OE and OEM parts are the same, though, as the OEM doesn't want to run two assembly lines.
In the case of the batteries, Johnson Controls I believe makes the OE battery under contract for VAG. Johnson Controls also sells batteries under a bunch of brands such as ACDelco, Energizer, Autozone, Interstate, and Pepboys.
It is arguably correct to say that the Energizer battery is OEM since it's manufactured by the same company that makes the OE battery and likely came from the same assembly line as the OE battery. (Though I'm not sure I buy that... Johnson Controls operates assembly lines all over... from New Jersey to China. I've yet to see evidence that the Energizer brand isn't coming off a lower quality line than the OE parts... clearly the OE and Energizer battery have different specs. They're both made by Johnson Controls, but how much does that matter?)