Battlefield Methane Tanks

The Grunt's homeworld is a methane planet and as such they breath a methane atmosphere. Thus when they are on an oxygen atmosphere like the Halos or Earth they need to wear a methane gas mixture.

When Grunts are in battle, they will run low on their supply of methane, so they must have a ready supply nearby.

Description
They are short and round in shape, purple in colour and have a large blue valve on top. They are seen generally where Grunts are operating. They only appear in Halo 2.