How do I use the battle packs? I have 15 unopened ones. Do I just open them? How long do they last?

Can surely open them in Battlelog,  but in game,  but escape to bring up the menu,  select balltpacks,  an down them.  Far as i can tell,  they don't expire if  unopened,  and went they give you,  you keep forever.  Well until you actually USE xp boosts.

They don't expire but they contain some useful perks. Some have upgrades to weapons ie grips, silencers etc. and some have 25%, 50% or 100% multiplier for xp points you earn in a match.