Hyundai Sonata Plug-in Hybrid / Kia Optima Plug-in Hybrid 9.8 kWh Battery

Reported failures, each from a source listed below, as of October 7, 2026.

• Owner complaints NHTSA lists under the Hybrid Propulsion System component for the Hyundai Sonata Plug-In, Kia Optima Plug-In Hybrid, by model year: 2016: 5 · 2017: 2. These are all hybrid system complaints, owner reported and unverified, not only battery faults, as of 2026-10-07.
• Hyundai TSB 17-HC-004 (December 2017) covers certain 2016-2017 Sonata Plug-in Hybrids built June 24, 2015 to August 31, 2017 that store DTC P1BA7 (overcharge detection active); the fix replaces the sub and main battery management system (BMS) units and wiring and updates on-board charger software. (static.nhtsa.gov: MC-10127010-9999.pdf, 2026-10-07)
• Hyundai service campaign TZ7 (TSB 16-01-008, March 2016) replaces the high-voltage battery cover on certain 2016 Sonata Plug-in Hybrids because the cover stud bolts may be corroded. (static.nhtsa.gov: SB-10074327-0699.pdf, 2026-10-07)
• Hyundai TSB 19-HC-001H (2016-on Sonata Plug-in Hybrid) links DTCs P1990, P1B76, P1B77 and P0A0D to the oil pump control unit wiring, power relay assembly and HEV safety plug. (static.nhtsa.gov: MC-10160095-9999.pdf, 2026-10-07)

Symptoms

• Hyundai TSB 17-HC-004 describes a 'Check Hybrid System' light with DTC P1BA7, sometimes with P1B77 or P1B25, on affected 2016-2017 Sonata Plug-in Hybrids. (static.nhtsa.gov: MC-10127010-9999.pdf, 2026-10-07)
• A keyword search of the 5 Hybrid Propulsion System complaints NHTSA lists for the 2016 Hyundai SONATA PLUG-IN finds that 5 mention warning light, 1 mention loss of power or reduced power, 2 mention stalling or shutting down (complaint text is owner-reported and unverified; as of 2026-10-07). (NHTSA complaints, 2016 Hyundai Sonata+Plug-In, 2026-10-07)

Hyundai's 2021 Warranty Coverage Guide lists lifetime battery coverage for the original owner of 2016-2019 Sonata Plug-in Hybrids, 10 years/100,000 miles for later owners, and 10 years/150,000 miles on the hybrid battery for cars certified SULEV/PZEV/TZEV in California-emission states; Kia Optima Plug-in Hybrid coverage was not confirmed from a Kia booklet. (static.nhtsa.gov: INRD-PE21010-15928.pdf, 2026-10-07)

How battery warranties work.