Audi Q7 PHEV (2017): diagnostics and balancing of the high-voltage battery

The hybrid Audi Q7 lost almost half of its electric range — instead of 40 kilometres on a single charge, it only managed 18. The customer contacted STS in time: this prevented serious battery degradation and costly replacement. The technicians performed diagnostics, detected voltage drop in two cells, charged and balanced the battery — and now it is working steadily again.

The PHEV (Plug-in Hybrid Electric Vehicle) system combines two energy sources — a traditional internal combustion engine and an electric motor with external charging from the mains. This format allows you to cover daily city routes on electric power and, if necessary, use the petrol engine for long journeys. The high-voltage battery plays a key role in this: its condition determines the mileage, dynamics, recovery efficiency and even the smoothness of the hybrid system. Therefore, regular diagnostics and balancing of the cells is the key to the long service life of the entire power unit.

The Audi Q7 PHEV is a flagship premium crossover that combines a powerful V6 3.0 TFSI engine with an electric drive. In its factory configuration, it can travel up to 40 km on electric power, offering the driver comfort, power and quiet operation. However, even in such technological systems, deviations may occur over time — and it was with this problem that the owner of the Q7 turned to STS in Warsaw.

Repair of an Audi Q7 3.0 PHEV with high-voltage battery problems.

A 2017 Audi Q7 PHEV with a 3.0 petrol engine arrived at the STS service centre. The hybrid system was still functioning, but the electric range had decreased from 40 km to 18 km. This is a typical sign that the battery is losing its balance between cells.

After an initial inspection, the car was carefully disassembled and the battery was removed and connected to an STS diagnostic stand manufactured in-house. A detailed inspection revealed deviations in the operation of two cells: a delta of 180 mV on a discharged battery.

For understanding: delta is the voltage difference between individual battery cells. If it exceeds the norm (usually up to 30-50 mV), the elements begin to work unevenly — some discharge faster, while others remain underloaded. Because of this, the electronics limit the total capacity, and the electric range is reduced.

STS technicians disassembled the battery, checked all modules, cells, the battery management block (BMB) and the monitoring system (BMS). No critical damage was found — the cells were found to be serviceable, they just needed recharging and balancing.

After equalising the charge, the difference between the cells was only 15-20 mV, which is an excellent indicator for a battery with mileage. The battery was assembled, installed in place, and tested. After servicing, the electric range increased to 33 km, and the system is working stably and without errors.

This case is an example of how timely referral to specialists can avoid costly repairs. Instead of replacing the modules, the customer received a fully restored, balanced battery and saved a significant amount of money.

The STS workshop in Warsaw has extensive experience with hybrid and electric systems, uses its own test benches, precision diagnostic equipment and in-depth knowledge of HV battery design. It is thanks to this level of competence that STS is considered one of the leading services in Poland, where owners of premium hybrids turn to with complete confidence.