Dissecting high-voltage batteries

Batteries are the powerhouse behind electrified vehicles, whether they’re hybrid, plug-in hybrid or pure EVs, so Technicians need to understand the technology. From how to make them safe to work on, to opening up the pack to fault find, it’ll give individuals and businesses the edge as more electrified vehicles hit the market and find their way into the workshop for maintenance and repair.  

Inside a battery pack

Understanding the components that make up a high-voltage battery pack is the starting point to mastering the technology. And while it may feel alien if you’ve spent the majority of your time working on combustion technology, you probably understand more than you think.

Just like an engine, they’re all basically the same, just with slight variations in their makeup to deliver slightly different performance and efficiency levels. Generally each pack will contain a host of components including:

• Individual cells; either as prismatic, pouch or cylindrical in design
• Busbars
• High-voltage charger connections
• Battery management controller
• Battery junction box
• Cell management controller
• Coolant connector
• Temperature sensors
• Crash sensors
• System main fuse

Fault finding

With over 1.5 million pure electric vehicles on UK roads (and many more hybrid and plug-in hybrid vehicles), and a burgeoning used market, the chances of one coming into the workshop is constantly growing.

Eliot Smith Founder and Lead Technical Trainer at Pro-Moto explains some of the reasons that the vehicle’s battery may need attention.

“Imbalance is one reason. You may get cells that start to degrade over long periods of time, but slightly quicker than others, so there’s a voltage imbalance. The battery management system is programmed to look at the balance and it will try and rebalance the battery, but at some point it will become excessive,” he says.

Another possible reason a vehicle’s battery may need maintenance is relays in the system.  

“Those relays sometimes fail, and then you need to replace either what you call the relay block or the contact block, or maybe individual relays,” says Smith.

One other example is water ingress. Although batteries are hermetically sealed and manufacturers do their best to minimise moisture entering the battery pack, it can happen. Smith gives one very specific example that could have been easily avoided.

“For hybrids where the battery's normally internal in the vehicle, they use the cabin air to circulate through the battery. There's a good case in Singapore where the national taxi service is run by the government, there's thousands of Toyota Priuses running around, and they were finding they were having battery failures,” says Smith.

“The taxi drivers were switching the air conditioning off and winding the window down, so you had humid air circulating through the battery. Then moisture built up inside the battery and that started to give incorrect readings inside the battery cells to the control unit, and corrosion on the control unit pins and harnesses.

Knowledge is power

Nobody wants to a nasty shock. So, with increasing chances that a high-voltage vehicle could need help in the workshop, how do you make sure you’re ready to work them?  

“One thing we do with level 2 and Level 3 qualifications is to prove the absence of voltage when the system is shut down,” says Smith. “But if you want to work on batteries you need to do your level 4 training.”

This qualification contains the knowledge of the dangers surrounding repairs carried out to high-voltage vehicle electrical components and systems. The aim is to provide technicians working on electric and hybrid vehicles with the required level of skills and knowledge to carry out repairs.

It’s been developed by IMI in conjunction with electric vehicle manufacturers, the health and safety executive, training providers and the IMI Sector Skills Council.  

Tools of the trade

A willingness to embrace new technologies is important as automotive electrifies, and with the right skills and knowledge in place, the next step is investing in the right tools. But Smith says this doesn’t have to be an enormous financial burden.

“I would recommend a Cat III multimeter from a reasonably good quality manufacturer. You need some insulation gloves, which we always tell people to use. Maybe some insulation tools because you're going to work on live batteries,” he says.

Smith also suggests investing in a good branded insulation tester, that could set you back from £300 upwards – they're specifically designed to test for a breach of insulation – but it can be used as a multimeter too.  

“You don't need a massive amount, but PPE is quite important,” says Smith.  

Working on high-voltage batteries is the next step in someone’s technical training for EVs and hybrids, opening up a host of new opportunities. Being able to detect and fix faults in packs means the ability to keep customers on the road, and with manufacturers becoming more open about their technologies, the maintenance market is likely to grow further with more replacement parts becoming available.

Benefitting from the expanding opportunities high-voltage battery technology offers will be down to embracing the technology, upskilling so you’re knowledge-ready, and investing in the tools.  

Find out more about the IMI’s Level 4 Award in the Diagnosis, Testing and Repair of Electric/Hybrid Vehicles and Components.