Truck electrical systems have become highly sophisticated with numerous microprocessors controlling many truck systems; engine operating management for fuel control, environmental/pollution, driver assist for Global Positioning System (GPS) navigation, driver alert surveillance of vehicles around the tractor, cab climate control, Anti-lock Brake Systems (ABS) and many more. It is critical that vehicle electrical systems have a stable voltage supply, and the battery plays a big part in this.


In North America, the most common voltage system used is 12 volts (V). The difference between the commercial vehicle and a consumer automotive battery system is that multiple 12-volt batteries are connected together in parallel to increase the Amp-hour (Ah) rating and give more cranking energy to handle a commercial vehicle’s significantly larger, more powerful engine.

Commercial vehicles can be put into two major categories: Heavy Duty (HD) automotive and HD truck. The automotive HD is the typical Ford F350 – F550 chassis principally using the Group 65 battery, the Chevrolet 3500 chassis using the Group 78 or 94R battery and the RAM 3500 using the Group 49 and 94R batteries. These are commonly used for applications like ambulances.

The HD truck market utilizes the Group 31 model battery in varying quantities depending on the size of the vehicle. Small- to medium-box trucks generally use two batteries, and vocational applications like HD dump trucks, waste haulers, cement mixers and over-the-road tractor trailers use three to four batteries.

Commercial vehicle batteries operate in harsh conditions and are expected to not only start high compression diesel engines but also provide power for hotel loads. Trucks used for urban delivery with non-idle restrictions and sleeper trucks with DC to AC power inverters can deeply discharge batteries due to the power drains. On a regular basis, batteries used in these applications can accumulate a large quantity of charge/discharge cycles annually.

Class 6 and class 8 trucks are being supplied with higher amperage alternators to meet the inter-city delivery starting and stopping loads. This is also necessary to address the increased hotel loads in sleepers as drivers want more entertainment and support systems.  

Know the Battery Type

Identifying the type of battery is important before addressing battery problems. There are three types of lead acid batteries used in commercial vehicle applications today: the maintenance-free flooded electrolyte battery, the AGM battery, and the Thin Plate Pure Lead (TPPL) AGM battery. Unlike maintenance-free flooded lead acid batteries that have liquid electrolyte, an AGM battery contains a glass mat separator made of fiberglass that is placed between each plate to absorb the electrolyte. This makes the battery spill proof with no additional water or electrolyte ever needed.

Premium TPPL AGM batteries, like ODYSSEY® batteries by EnerSys®, use pure lead, allowing an ODYSSEY® battery to have thinner plates. This allows more plates to be used, increasing the surface area exposed to the acid and generating more power from the same size battery.

Preventing Battery Problems


Fleets should prevent batteries from becoming extremely deeply discharged – dropping to less than 10 volts due to extended storage with vehicle support loads. Also, trying to start trucks with a low state of charge or weak capacity batteries can cause high amperages and low voltages. This can overheat the starter motor and can damage battery cables.

When a truck comes in for periodic maintenance, technicians should test each battery, looking for consistent tested values or to see a reduction in previous performance. This can help to spot a potential problem battery before it can cause a no-start condition on the road.

A voltmeter on the battery terminals will indicate the battery’s State of Charge (SOC).

State of Charge

Flooded Battery

AGM Battery

TPPL AGM Battery






















After starting the vehicle, the voltage on the meter must indicate that the alternator is delivering between 14.00 and 14.40 volts when measured at the battery’s terminals. Initially, the voltage on the terminals may be low if the SOC of the battery is too low and the voltage will climb to a stabilized voltage as the battery SOC goes up and at this point, the battery terminals should read between 14.00 and 14.40 volts. Alternators should provide a regulated charge no lower than 14.00 volts and no higher than 14.40 volts to prevent premature failure of the battery. A link is provided at the end of this article to download the ODYSSEY® Battery Technical Manual for details on temperature compensation.

Charging systems on all vehicles usually operate at 14.20 volts; the charging system output amperage is what differs. Output amperage on small vehicles can be less than 100 amps and go up to 300 amps on large HD trucks. Some applications like transit buses can have over 500 amps of output.



One of the most common service mistakes is using the incorrect method of charging for the battery type. Old-style linear chargers that apply charge voltages greater than 15.0 volts are not recommended on modern maintenance-free or sealed batteries due to overcharging and the possible loss of electrolyte.

Modern, “smart” battery chargers have the ability to sense the battery condition and adjust the charging rate accordingly. They also have been programmed with a charging algorithm to adjust the charge voltage and amperage during the charging process.  Charging should always be conducted in a ventilated area.

The best strategy for reducing battery issues

The best and most effective defense against high cycling with deep discharging is to incorporate large amperage alternators. This provides the fastest recharge to full charge on the batteries. Boost charging batteries during vehicle maintenance procedures with high power chargers can bring batteries back to full charge at least a few times each year. Take rested voltage values of each individual battery to look for voltage value consistency between each battery. This will help identify any battery with a lower voltage value that might be failing.

Fleet managers are increasingly willing to pay more to include a long life TPPL AGM battery in their new trucks. They have found that these batteries usually will last the life of the trucks’ service window for the first owner, thus being a net cost saving. In addition, the TPPL AGM helps reduce additional costs associated with unexpected no starts. The TPPL AGM batteries offer significantly longer service life: generally, 30 months to 60 months. The use of pure lead significantly reduces plate corrosion. And, a TPPL battery with tin-plated brass terminals requires no terminal maintenance.

Technicians may refer to the ODYSSEY® Battery Technical Manual as a good source of information about how ODYSSEY® batteries work, and their proper testing and maintenance. A copy may be downloaded at:

Conclusion – Know Your Facts
Premium AGM batteries with TPPL technology, like ODYSSEY® batteries, offer more power and longer life to handle today’s toughest vehicle demands.

Find out how ODYSSEY batteries can help your fleet and maintenance managers to start saving today. Visit to learn more or to request to be contacted by a sales representative.

About the author
Oliver Patton

Oliver Patton

Former Washington Editor

Truck journalist 36 years, who joined Heavy Duty Trucking in 1998 and has retired. He was the trucking press’ leading authority on legislative and regulatory affairs.

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