Let us paint you a picture. It might be familiar to you.
It’s 6am and still dark. You can see your breath in the air as you rub your hands together to try to stay warm. All around you, the vans are starting up to begin their long days of deliveries.
All, that is, except one. You could jump it, but what if it dies mid-route?
And with that, your entire day’s plan immediately falls apart. You’ll put that cup of tea down and forget about it until Noon and it’s stone cold. There’ll be no time for a breakfast break. You’ll be working non-stop to get that van out on the road, and then you’ll be onto all your regular maintenance jobs.
What if all that could be avoided with some simple state of charge battery checks? Here’s how to go about it.
Why does state of charge matter more than a voltage check?
It’s easy to default to battery voltage checks. That’s not a bad thing. Voltage tests can highlight developing problems and give you a rough idea of the charge. However, it’s not perfect and doesn’t reliably show the battery’s risk of failure or the underlying condition of its chemicals.
A voltage reading right after the engine turns off, or right after a charging session, can include surface charge. This raises the terminal voltage without meaning the plates necessarily hold much usable charge.
We recommend state of charge (SoC) checks as standard instead. You’ll need a battery tester that checks for SoC. Unlike basic voltage tests, SoC gives you a repeatable baseline with a better idea of how much charge is present at that moment. Advanced testers may also measure the internal resistance, reserve capacity and charge acceptance at the same time. These can give you a much better idea of how well an automotive or marine battery is performing, and whether it needs further testing.
Being ahead of this means you can replace or recondition the battery long before that fateful 6am failure to start.
How do fleet workshops check SoC?
The first and most important thing to define is the battery type. For example, a 12-volt flooded is very different from an AGM-type, and a 24-volt truck or bus system also requires a different approach.
Once you know the right battery chemistry and duty cycle, you can select the right battery tester or choose the correct settings on your existing tester.
Attach it to the terminals, and the device should output a percentage reading with an actionable result: either ‘Pass, ‘Fail’ or ‘Retest’ (or words to that effect). It’s that simple.
These testers may also provide you with a few other useful readings, such as state of health (SoH). SoH does tend to overlap with SoC in many ways, because it represents how much of the battery’s original capacity is still available. If your tests reveal either low SoC or low SoH, conduct some further investigations. (Low SoH is a greater risk than low SoC.) In the meantime, fit a replacement battery to the fleet vehicle.
What SoC reading should trigger action in a fleet?
Before using any rule of thumb, set your own SoC limits. Look at your past data in ROBIS. Find the SoC level where vehicles start failing to crank. Then set your service trigger at that level, so the battery gets checked before it causes a no-start. Here are a few SoC readings that indicate a battery might need some extra attention:
- 12-volt lead-acid/AGM/EFB battery – many workshops treat 75% SoC as the point at which they charge and thoroughly test it.
- 24-volt systems – as usual, treat the two 12-volt batteries individually. If one of them drops below 75% SoC, test, recondition, and retest both batteries. Then recheck the balance as a pair.
- Storage and standby vehicles – boost the charge once SoC drops to around 70% to limit plate sulphation.
It’s worth noting here that as standard, Midtronics testers don’t give out an SoC percentage reading. They display ‘decisions’ instead, such as ‘Good Battery’, ‘Good – Recharge’ or ‘Bad Cell’, etc, to indicate when a battery is good to use and when it might need recharging, repairing or replacing.
If the battery seems fine, check for other electrical draws like alternator faults, parasitic drains and idling issues. Also, compare this with your route data to see if there’s any correlation.
And all this brings us back to the van that refuses to start at 6am on a dark morning. You don’t need to develop a perfect way of measuring every single battery statistic. The goal is simply to minimise the risk of mornings like this happening. All it takes is a small adjustment to your servicing and maintenance routine, and you’ll have a clear idea of how all your fleet batteries are performing, and know when to act.
Here at Rotronics, we supply fleet operations like yours with industry-leading battery testers and chargers. Use these as part of your workshop management system to establish a battery’s SoC and SoH.
For more information about our models and which best suits your setup, get in touch with us today. We’ll help you find the perfect model to meet your vehicles, your maintenance plans, and your budget.
