Card power mechanism

A fresh new minted card will have 100% power by default. After each transaction, the power of the card will decay depending on the Capacity point of the card.
PowerDecay=f(Capacity),CurrentPower=100PowerDecayPowerDecay=f(Capacity), CurrentPower=100 - PowerDecay
Recharging the card back to full power will depend on the current power and the amount of STE earned. To recharge the power of any card to 100%, users have to spend STE:
RechargeFee(STE)=f(CurretPower,STEEarned)RechargeFee (STE)=f(CurretPower, ∑STEEarned)
Note: Users must spend a small amount of NEXT for each recharging. Recharging cost = $0.2 equivalent