How to extend battery life

Gale Kimbrough, engineering and technical services manager at Interstate Batteries (,  the number one replacement brand battery in North America, offer these maintenance practices and tips fleets should follow to can assist them in insuring extended battery life:

1. Visual Inspection of the batteries on a consistent basis.

2. Proper battery care and consideration.

  • Keep the battery's polypropylene surface clean. If the battery's top surface gets dirty it can often allow a low level parasitic current draw between the negative and positive terminals which discharges the battery quicker.
  • Keep the battery terminal's clean. Terminal corrosion increases electrical resistance creating a power loss.
  • Test the battery's state of charge and recharge when necessary. Every 200 millivolts (0.2V) drop in static voltage level reduces the battery's state of charge by approximately 20 percent. 

3. Know and understand the battery's state charge level.

Lead Acid Flooded Batteries

Voltage vs. State of Charge




100 percent


75 percent


50 percent


25 percent



4. Test/evaluate the electrical system properly - battery, starting and charging.

  • Use the correct tools
  • Make sure technicians have the proper training.


"I was in Indiana is the fall to troubleshoot some potential battery/charging systems for a fleet," recalls Kimbrough. "While I am there I noticed four trucks being brought in to the shop for a PMI (preventive maintenance inspection). The technicians were going around the truck testing various areas and at one point tested the batteries.  

"I slipped over and tested the batteries myself. The four battery systems tested between 12.22V on truck #1 to a high of 12.34V on truck #4. Not understanding or having the training on a battery's state of charge versus voltage, the technicians did not place a charger on the batteries during their PMI.

"In conducting the PMI, they left various lights on while they greased and changed oil which added to the battery discharge level."

Several hours later, Kimbrough tested the batteries prior to the technicians releasing the vehicles for use and found 12.02V on truck #1 and 12.22V on truck #4. He asked the technicians to recharge the batteries prior to releasing the vehicles. Their reply: "The trucks are starting. We'll let the alternator recharge the batteries."

  • 12.02V. These batteries are discharged to 100 percent of their capacity, he explains. Considering each Group 31 battery is rated at approximately 100ahs plus 15 percent, then 100ahs x 4 batteries x 1.15 equals 460ahs and will need to be replenished.
  • 12.22V. These batteries are discharged to 75 percent capacity. 75Ah x 4 batteries x 1.15 (extra 15 percent) = 345ahs; need to be replenished.

Considering the charger averages 20 amps input, #1 truck batteries require 23 hours and truck #4 will require 17 plus hours, says Kimbrough, and offers these tips:

  • Check the batteries.
  • Have a battery chart posted.
  • Place a charger on the batteries when conducting a PMI.
  • Never expect the alternator to recharge the batteries.