Stump the Chumps Q&A: Opportunity Charging

I was taught that it’s necessary to fully discharge a battery before charging it. Why now is i

I was taught that it’s necessary to fully discharge a battery before charging it. Why now is it okay to opportunity charge batteries during any break time?

The viability of fast and opportunity charging technologies has been established through years of extended field trials and actual usage, yet there are still some common misperceptions. Let’s take a look at the facts:

Conventional charging has its drawbacks

Consider a multi-shift battery changing operation using conventional charging and following the (old) 888 rule. The 888 rule dictates that each battery undergoes 8 hours of discharge, 8 hours of charge, and 8 hours of rest. What does this mean for the batteries?

Over discharge

  • An electric forklift truck battery will typically be depleted to a 20% state of charge (SOC) in one eight hour shift, sometimes dropping below 20%.
  • Below 20% SOC, truck performance significantly deteriorates and battery damage may occur.
  • Most battery warranties are voided if the battery is discharged below 20%.


  • Conventional charging tends to overcharge batteries at each charge cycle, causing excess energy loss due to periodic gassing.
  • While PowerDesigners’ chargers compensate for battery temperature, most conventional chargers do not.

Preserving battery life with fast and opportunity charging

When employing opportunity charging, fast charging during operator breaks provides quick periodic refueling of batteries and ideally maintains battery SOC in the 40% to 80% range throughout the workday.

Most skepticism about opportunity charging arises from the fact that batteries do typically operate at higher temperatures with opportunity charge applications. However, the battery’s temperature remains within manufacturer’s guidelines and modern smart chargers are equipped to limit or stop the charger output as battery temperature increases, water levels become low, cells become weak, or the battery does not transition through the charge cycle as expected. Smart charging that actively measures temperature and manages the current and battery voltage optimizes charging while significantly minimizing gassing, preserving battery life and delivering the greatest amount of energy back to the battery.