When should a fleet replace vehicle batteries?

Should you replace on a failed test or a failed start?

On a failed test. The aim is to replace each battery after a test shows it's weakening, and before it strands anyone (our framing). For one driver, a dead battery is a bad morning. For a fleet, it's a vehicle that can't go out, a driver waiting and a job that slips.

Two facts set the timing:

• Age. The Canadian Automobile Association warns that a battery "between three to five years old ... could fail."
• Season. Varta, the Clarios battery brand, says heat "dramatically shortens the life-span of a battery," so that by winter older batteries "are close to their limit." It advises having batteries checked "at least once a year before winter."

So a yearly pre-winter test is the minimum, and batteries from about three years old deserve closer watching.

Three ways to plan replacement

The table is our analysis, not from a source. For most small fleets we'd combine the last two: test every battery before winter and at each service, replace any that fail, and set an upper age limit for vehicles where a no-start would be especially costly, such as the one that opens the shop.

Why do fleet batteries age differently?

Fleet use is harder on batteries than you might expect, in ways that differ by vehicle:

• Short trips. Varta says that when a car is "used infrequently or only for short distances, the alternator cannot fully charge the battery." Delivery and service vehicles that start and stop all day can end up undercharged (our inference from Varta's point).
• Vehicles that sit. A spare or seasonal vehicle drains slowly while parked. See how long a car can sit and parasitic battery drain.
• Heat. Varta names +20 °C (68 °F) as optimal; hot climates and hot engine bays age batteries faster.
• Cold. Cold cuts the power a battery can deliver just as the engine needs more. See why batteries die in cold weather.
• Extra loads. Upfitted vans with lighting, inverters or tools draw more (our note).

How do you test a fleet battery?

1. Resting voltage

Measure across the terminals after the vehicle has sat for a few hours with everything off. East Penn's Battery Care & Maintenance guide gives this chart:

East Penn says to charge any battery reading below 12.4 V. Resting voltage shows charge, not health: a worn battery can read 12.6 V and still fail under load (our note; that's why the load test follows). For more on reading voltages, see our battery voltage chart.

2. Load or conductance test

A load test shows whether the battery can deliver current. East Penn's procedure:

1. Charge the battery fully first. "You can't load test a discharged battery."
2. Set the tester to half the battery's cold cranking amps (CCA) rating and apply the load for 15 seconds.
3. Read the voltage at 15 seconds. At 21 °C (70 °F) or warmer, a good 12 V battery holds at least 9.6 V; the minimum falls with temperature, to 8.5 V at −18 °C (0 °F).

CCA is the current a new, fully charged battery can deliver for 30 seconds at −18 °C (0 °F) while staying at or above 7.2 V, per Battery Council International. Handheld conductance testers are quicker, but East Penn notes they are "ineffective on a discharged battery," so charge first with those too. For AGM batteries, use a tester with an AGM setting.

Safety. East Penn's first instruction is to wear eye protection. Batteries give off explosive gas, so keep sparks and flames away, connect the tester with it switched off, and never charge a battery that may be frozen (East Penn warns it can explode). We'd also not test or charge one with a cracked or bulging case; replace it (our advice).

3. Record it

Log every test by vehicle: date, resting voltage, test result and battery install date. A battery whose results slip from one test to the next is the one to replace before winter (our suggestion).

How do you replace a fleet battery correctly?

• Match the specification. Ford's US 2018 Escape owner's manual says to use a replacement "that matches the electrical requirements of your vehicle," and that for vehicles with Auto-Start-Stop "you must replace the battery with one of exactly the same specification." Other makers have their own rules; check each vehicle's manual.
• Follow the maker's procedure. The same manual says to wait at least two minutes after switching off before disconnecting, to disconnect the negative (−) cable first and the positive (+) last, and warns the transmission may shift firmly at first while it relearns. Some vehicles also need a battery-monitoring system reset after a new battery (our note); that varies by maker, so check the service information.
• Don't let stock go stale. East Penn tells stockists to rotate batteries first in, first out, store them upright somewhere cool and dry, and says stored batteries need routine charging; it suggests testing stored flooded batteries every 4–6 months. A fleet that keeps spares should do the same, and read the date code before fitting one.