Make sure that there is no physical connection between weapon and PKs. The player can assume that weapons are recharged via something like induction. Let Forerunner weapons recharge when near crates or Prometheans.

Play test to establish how near you need to be to get a recharge. Level designers can establish areas of feast or famine. Areas that you can camp in for a while with infinite ammo, and no-recharge areas that you need to cross in order to take the fight to the enemy.

This gives you a new, area based, mechanic. Have a visible indicator on HUD and/or weapon that lets you know if you are in range of a charger. Maybe have a WI-fi/Signal-strength indicator. High signal recharges almost immediately. Low signal takes time to recharge shots.

People understand signal strengths. AFAIK this is a new weapon mechanic but builds on top of area control and can encourage getting close to enemies. Close is dangerous but has a reward. Kill most crawlers but let some near to recharge. Maybe more powerful enemies recharge your weapon faster.

Thoughts anyone?