One opinion on the subject from a Spark EV Forum
Don’t get your hopes up! For the 2016 model, the battery must degrade more than 40% and / or within 8 years from the date the car was first put into service. I estimate the 2016 Spark EV battery capacity must fall below 11.4 kWh before the warranty is valid. AND… "if warranty repair requires replacement, the high voltage battery may be replaced with either a new or factory refurbished high voltage battery with an energy capacity (kWh) storage) level at or within approximately 10% of that of the original battery at the time of warranty repair."
REF: Page 14 of the 2016 Chevrolet Limited Warranty and Owner Assistance Information booklet.