As a fleet manager, which are your technicians’ least favourite times?
The January days when the workshop simply never warms up? Or the August days when it never cools down?
Neither are pleasant to work in. But the temperature is affecting far more than your team.
Both hot and cold temperatures impact a 12-volt battery’s ability to hold charge, although here in the UK, we’re usually more worried about the cold weather than the hot. And you’ll be familiar with that sinking feeling as the first vehicle off the lot in December tries to crank several times, then rattles as it gives up.
That puts a delay on everything else. The driver has to wait. The technicians have to adjust their schedule. Routes fall behind, and customers start getting impatient. Other repairs get pushed back. And all of this before your working day begins.
Compensating for these temperature changes in your batteries can prevent an awful lot of these morning headaches. Here’s everything you need to know.
How cold affects battery performance
The ions in the electrolyte move more slowly in the cold. As a result, electrode reaction rates slow, while ohmic and charge-transfer resistances increase, causing greater internal resistance. The long and short of it is that you get far less current flowing to the starter motor and other systems, so the engine cranks slower. And, if there isn’t enough charge, it might not crank at all. Accessories may not work as expected, too.
Lead-acid batteries are most susceptible to cold. A fully charged battery at 0°C delivers roughly 50% to 60% of the power it would at 25°C. Partial state-of-charge (SoC) and repeated cold starts accelerate sulphation on the plates, so you get even less capacity over time.
AGM batteries handle the cold slightly better than EFB or standard flooded lead-acid. Lower internal resistance allows higher current delivery in sub-zero temperatures. EFB batteries still work in the cold, but struggle more with repeated deep cranking cycles.
Practical guidance for fleets in winter: park your vehicles indoors when possible, and keep the batteries as close to room temperature as possible. Use trickle charging to maintain full charge if a vehicle isn’t in use, ensuring the charger is appropriate for the battery chemistry. Schedule battery checks before and during the coldest months to identify any units that are starting to struggle.
How heat impacts battery life
On the flip side, high temperatures speed up the chemical reactions inside the battery, including the useful reactions and the side reactions that damage components. It doesn’t take long before the unwanted side reactions start taking over.
Before long, your technicians will start to notice the effects of lead plate corrosion, electrolyte evaporation and positive plate shedding. These negative processes occur much more quickly at elevated temperatures. Over time, these processes can reduce the battery’s ability to hold charge and deliver current.
As a broad (and somewhat oversimplified) rule, a 10°C increase above 25°C roughly doubles the rate of chemical wear inside lead-acid batteries. Operating at 35°C for one month can be as damaging to a battery as operating at 25°C for two months.
And just a quick note that it’s the battery’s operating temperature we’re talking about. Sometimes, even if it isn’t particularly warm, the battery might start overheating. This could be due to an overheating engine, another issue in the engine bay or an internal fault in the battery itself. Of course, this creates a vicious cycle. Regular testing, as discussed below, might be the only way to identify any red flags.
EFB batteries tolerate heat marginally better than standard flooded types because they’re less prone to heat-induced drying and corrosion than AGM types. Still, that doesn’t mean they’re immune to the effects of heat. Repeated operation at high temperatures still reduces battery life, regardless of the battery’s chemical composition.
Practical guidance for fleets in summer: park your vehicles under cover to avoid prolonged exposure to direct sunlight. Consider thermal shields or insulated battery boxes if your vehicles are left outside for long periods. Ensure your chargers are correctly set to prevent overcharging in hot conditions. In the UK, the heat isn’t usually as much of a worry for batteries as the cold winters.
Maintaining performance across the seasons
An in-house battery management system is the most effective way to monitor the performance of your batteries. Have your technicians conduct routine, scheduled checks for voltage under load, conductance and internal resistance. These tests reveal the earliest signs of reduced capacity.
The testers you use should come from reputable companies and sync with software, such as ROBIS, to log results and track performance trends across the seasons. Over time, as you build up more data and compare it with data from others, you’ll start to get a real-life picture of your fleet’s batteries and which units are performing better than others, and in what contexts.
At Rotronics, we work with fleets across various industries, including logistics, emergency services and more. We know that preventing temperature-related battery issues requires just a few simple steps, including monitoring, proper charging, thermal protection and periodic testing, to keep most of your vehicles starting reliably all year round.
Get in touch with us today about our battery testers, chargers and how to optimise your battery management activities for the upcoming winter season.
