When your implant runs out of energy why not have the implant still work just a lot less well. For example you have the health regeneration and run out of energy. The implant will still heal you. Just much much more slowly than if it had enough energy. Safe landing could let you still survive a drop just a smaller one without energy. The mine detection implant would still work just at a shorter range. And so on. This would allow a player who doesn't make much xp and consequently doesn't gain much energy chargers to still benefit from the implants. But to get the full benefit you need energy so there's still a reward/benefit to gaining or buying chargers.
