Project Gemini – Making KIA Soul EV immortal from SK 28kWh to Panasonic 35.3 kWh battery

Project Gemini – Making KIA Soul EV immortal from SK 28kWh to Panasonic 35.3 kWh battery

The first-generation KIA Soul EV (2015) was KIA’s first mass-produced electric vehicle – well built, high quality, and generously equipped. However, it suffers from one serious and widely known flaw: catastrophically poor SK Innovation pouch-cell chemistry.

The battery uses cells with a nominal capacity of 35 Ah, configured as 2 cells in parallel and 96 series strings. In a large number of cases, battery failure occurred before 50,000 km. Battery cooling is air-based, drawing air from the cabin through intakes located beneath the driver and passenger seats, with forced exhaust to the outside via a fan. In this way, battery temperature is regulated by cabin temperature in both summer and winter.

The core issue, however, is not cooling, but cell chemistry and poor structural module design. The upper cells in the battery pack consistently fail first – all top-layer cells in all eight modules. An additional problem is the highly non-standard and commercially unavailable cell format (approx. 35 cm × 13.75 cm × 10.5 mm). Furthermore, the cell terminals are copper on one side and aluminum on the other, making soldering impossible; interconnection requires laser welding only.

A new 30 kWh OEM battery from KIA costs approximately €24,000 + VAT and, according to recent information, is now unavailable. This is the same battery that should have been globally recalled due to dangerous cell swelling, not limited only to the USA and Norway, where other owners were effectively discriminated against. Repair of the original battery is technically possible only by cannibalizing another failed pack—cells from the lower module zones must be transferred to the upper zones, where original busbars no longer fit and require welding old busbars onto replacement cells.

The internal resistance of failed parallel groups frequently exceeds 1.5 mΩ, and it is not uncommon for more than 16 groups to fall outside specification, requiring replacement of the entire upper layer. In practice, such repairs last no more than 1–1.5 years, after which the next layer begins to fail. For this reason, we concluded that conventional battery repair is fundamentally unsustainable.

To prevent the vehicle from being scrapped, we developed a retrofit solution using new, homologated, and certified Panasonic modules sourced from the Mazda MX-30. These are 6S2P modules with a 2.21 kWh gross capacity each. A total of 16 modules were installed into the original KIA Soul battery housing, resulting in a 96S configuration and 35.3 kWh gross capacity.

The primary engineering challenge was air cooling from the cabin. Despite the fact that, due to much lower internal resistance and higher C-rate, these cells generate virtually no heat during charging or discharging, we chose to retain active cooling. The modules are mounted in the exact positions of the original modules, matching the original envelope dimensions, and fixed to factory mounting points. Between the two module rows, a PVC air duct was installed to guide cabin air toward the lower section of the battery enclosure and modules, ensuring even and controlled airflow across all zones, which was validated through simulation on a real vehicle. The modules are additionally raised more than 3 cm above the base, improving safety in the event of mechanical impact.

The final step involved LV wiring. Using original battery system connectors, we produced adapter harnesses to transition from SK Innovation to Panasonic modules, ensuring that all LV components, connectors, and wiring remain OEM and certified. The only modification was on the HV side, where custom busbars were manufactured manually. PTC temperature sensors were placed at multiple points—on busbars and on the modules themselves—so that in the event of overheating, the system immediately opens the contactors. The BMS, protection logic, and all electronic safety systems remain completely original and unmodified.

After full assembly and connection of LV and HV wiring, the system powered up successfully on the first attempt, initially tested on a lift prior to vehicle installation.

Given that the “sustainability” offered by KIA proved unsustainable in practice, the only way to make the vehicle truly sustainable was to make it better than original. The new 35.3 kWh battery delivers approximately 155 km of range at 0 °C with an average consumption of 19.8 kWh, until turtle mode activates. With approximately 5% remaining SOC, an additional ~20 km is achievable. After several charge-discharge cycles required for SOC calibration, real-world summer range increases to approximately 250 km.

We are opening module sales to third-party service centers, enabling them to perform the same retrofit. Material cost is approximately €3,300, with 80–130 labor hours, depending on workshop capability.

We have produced one complete battery, ready for sale following road testing.
Price: €6,000 + VAT

Extending the service life of electric vehicles through retrofits and upgraded components is not only possible, but essential for real sustainability. With proper engineering, education, certified training, and homologated components, such solutions are fully achievable, safe, and economically viable. While the EU and OEMs largely promote sustainability on paper—through regulations, targets, and marketing—it is third-party specialists and the wider repair ecosystem that actually deliver sustainability in practice. Keeping vehicles on the road longer, preventing premature scrappage, and enabling responsible upgrades has a far greater environmental impact than producing new vehicles or replacing entire battery packs. True sustainability is not declared; it is engineered, validated, and implemented.

Comparison:

• Original battery degradation: ~70%
• OEM battery: €24,000 + VAT → ~100-150 km range
• EVC retrofit: €6,000 + VAT → ~155-250 km range

Part number: 37501-E4000

Ordes for KIA Retrofit will be done on Zagreb and can be purchased thru email [email protected]

PANASONIC 6S2P 2.21kWh Prismatic