NOTE: These instructions are meant to be a guide for Hybrid Automotive Prolong Battery Charger owners. Every hybrid battery is different and will exhibit its own unique charging/balancing patterns. Your experience may vary from what is listed below. We offer no guarantee that the below instructions will work exactly as described for you.

Safety Precautions:

  • Never charge when ambient temperatures are over 100 degrees Fahrenheit (38 degrees Celsius)
  • Try not to use charger when vehicle is parked in direct sunlight
  • Leave vehicle windows open if at all possible to provide ventilation

Prolong Battery Charger Instructions:

Refer to the Battery Reconditioning Overview for a summary of the hybrid battery reconditioning process.  These instruction focus specifically on the battery charge & balance cycle.

The car should be turned off while charging.  The first phase of charging is ‘filling’ the battery. When you begin the charging process the hybrid battery will be somewhere between 40%-80% charged (Toyota) or 20%-80% charged (Honda) depending on how full the battery was when you parked the car. During the ‘filling’ phase the voltage displayed on the charger will slowly climb at a steady rate from the starting voltage to a 100% charge level, then level off. The max voltage of your battery will vary depending on vehicle model, its overall condition, and will likely change from charge session to charge session. Refer to the below table for typical hybrid battery peak voltages by vehicle.  It can take anywhere from 4-16 hours for ‘filling’ to complete, depending on how drained the battery charge is when you park the car.  (Note: no ‘balancing’ occurs during this ‘filling’ phase.)

Once the battery becomes ‘full’ the balancing process will begin.  During the ‘balancing’ phase you will most likely see a steady voltage reading or a very slow oscillation of voltage – perhaps a 1-3 volt swing over several minutes. This means the battery is in the balancing phase. The initial balancing can take 4-12 hours after the filling phase is complete. Subsequent balancing sessions will likely be much shorter, perhaps 4-6 hours after filling is complete. During balancing, each individual hybrid battery cell is rising to a true 100% state of charge. As an individual cell reaches its peak voltage it warms slightly, then the voltage drops as it converts the excess charge energy to heat, then the cell cools and again charges to 100%. The process is repeated over and over. (This is why proper battery cooling is so important).  As the higher voltage cells undergo this cycle the lower voltage cells continue to fill and ‘catch up’ to the cells that have already reached 100% charge level. This is how the hybrid battery pack as a whole becomes re-balanced. Once the voltage no longer fluctuates, and/or the desired amount of time has elapsed, the charging and balancing process is complete.

A completely empty pack takes just under 24 hours to reach a full state of charge and balance, depending on cell efficiency. At no time should the combined ‘filling’ and ‘balancing’ times exceed 48 hours.

At this point you are done charging and can disconnect the charger. If you are reconditioning the pack, this is when you will want to connect the discharger and start draining the pack.  Refer here for the Prolong Battery Discharger User Guide or here for the Light bulb discharger User Guide.  If you are not going to discharge the pack, we recommend waiting 30 minutes after disconnecting the charger before driving the vehicle.

Optional Step: If your vehicle allows, you can reset the hybrid system to allow the vehicle to immediately see the new charge level of the battery pack. On the 2000-2006 Honda Insight, The IMA system can be rest by either: (1) removing the IMA fuse for 60 seconds, or (2) disconnect the 12v under-hood battery for 60 seconds. For all other vehicles, the 12V under-hood battery must be disconnected for at least 60 seconds.  Then reconnect the 12V battery/IMA fuse, start the car and allow it to idle. It is normal for the car to show zero or low bars for the hybrid battery and force charge the battery for two to ten minutes after resetting the hybrid system as it recalibrates and recognizes the new charge.

Battery Charge Voltage Table:

Single Cell99-03 Prius04-15 Prius06-15 Camry Hybrid

00-06 Insight

03-05 Civic Hybrid

05-07 Accord Hybrid

06-11 Civic Hybrid09-14 Insight

06-13 Highlander Hybrid

Chevy Silverado/ Tahoe Hybrid

Lexus RX/
GS Hybrids

Number of cells in battery packOne22816820412013284240
Normal Operating Range
(Filling Phase)
Peak Voltage Range
(Approx. voltage of balancing phase)

Prolong Battery Discharger User Guide

Light bulb discharger User Guide