I charge mine 100% every time!
I'm not sure about other countries but here in US, Hyundai has Lifetime Battery Warranty. I called the Hyundai customer service, they told me that the battery warranty is "up to the dealers" to determine if it can be covered under warranty. I called the local dealer, they said it depends on the situation, they need to test the battery to find out.... blah blah blah....
Too many things to think about, so I just made it simple. I charge 100%. so far I have no issues I've had my car for 5 months now. I figured that if the battery fails, i just have the dealer replace it.
If you’re happy with that, that’s fine. Although from my readings “lifetime” in USA is not defined, and can be as little as 4 months for some products. But what concerns me is the deterioration, rather than absolute failure, of the battery. I only picked up my Kona MY2020 last week, but have been driving a (Mitsubishi) PHEV for some years & that has made me more cautious with traction batteries.
The Hyundai warranty on traction batteries, at least in Aus, is that they will retain 80% charge after 8 years. Mitsubishi has a similar warranty. That sounds about where I was heading with my PHEV that I generally charged to 100% each time. A 100% charge when new gave me about 50km range in summer & 40km in winter. After 5 years this had reduced to (about) 40km in summer & 30km in winter.
There was no sign that the batteries would fail entirely, so there were no grounds for a claim against the 8 year Mitsubishi battery warranty. But the distance I could get on an icy morning was getting to the point that I couldn’t make the 23km round trip to work without using the ICE.
From my research, the remedy for this loss of charge/range in Li batteries is to exercise some care in charging. Doesn’t have to be onerous though. Simply keeping battery charge between 20 & 80% most of the time as suggested here should mean the car will keep its range a lot longer. As the Kona has a big battery this should rarely affect driving.
While we still don’t know the cause of fires in Teslas (& one Kona in Canada) I note that Tesla is reducing max charge in their older models X & S to 80% as a precaution. While that caution may prove unnecessary it gives me another incentive to minimise charging to 100%. Likewise Apple iPhone software (currently in beta for release in next update) will introduce rapid charging to 80%.
Everyone is different in their demands on cars & if you want to charge to 100% every time that’s fine. If you’re only doing short trips there should be no noticeable problems. But I want to do some trips that will challenge the kona’s range over coming years & want to retain the ability to do this.