It's not really easy to die in battle anymore to make it to Valhalla. In the Norse religion it wasn't seen as a good thing to be old, you wanted to battle and die to make it to Valhalla. Otherwise you'd end up with
Loki Hel in the underworld.
This thread makes me excited for the 3rd season of Vikings coming out this month!
Fixed that for you.
Hel isn't a place, Hel is Loki's daughter. Hel rules over vast mansions with many servants in her underworld realm. Loki was bound in the Underworld until the cosmos was destroyed during Ragnarok. My statement was accurate, you didn't need to "fix" anything.
This picture shows Sigyn, the wife of Loki, stopping the dripping acid of the serpent being dripped on Loki to release him from the pain while in the underworld where he is being held until Ragnarok.
Hel controls the underworld, where those who die a dishonorable death go. This includes people who die of old age.
Valhalla is an afterlife destination where half of those who die in battle gather, the lucky ones go here. If you are blood eagled and don't scream, you'll go to Valhalla also to fight with the other lucky warriors along with Odin and Thor
Fólkvangr is an afterlife field ruled over by the goddess Freyja, who chooses the other half who die in battle to reside with her there.