All objects that you can collect as a Scavenger will give their resources to nearby allies. Think of them not as chests that you take something from, but rather as dispensers that dispense their content to anyone who happens to be close enough.

Works with ammo crates (yellow boxes), power core boxes (blue), medkits and blood piles. Yes, this means you can get a total of 25 blood from a single blood pile if all five scavengers stay around it.

So next time you get to a blood pile, press Q (by default) to ping your location so that a nearby scav could get blood too. If he is already full/occupied with something else/deaf and blind then just take it all for yourself, I guess.

This may seem like an obvious feature but I haven't found this info anywhere in the game, and I still see people avoiding blood piles that someone else is already running to.

That's pretty much it, thanks for your attention, have fun and don't bully hunters