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Hi,
I am the owner of a 2020 Kona EV. I got the new battery in July 2022 and have noticed an odd behavior this winter. When I set the car to charge immediately after plugging in (which is after driving), the range tends to go down and the mi/kWH also goes down. I got an OBD2 dongle and used Car Scanner to look into it and it told me I had 9.8% degradation after only 11000 miles on the new battery. Then, I switched to delayed charging after 10 pm (2-3 hours after plugging in). Since then most of the range has come back and the mi/kWH has also risen. To me, it seems the battery or BMS doesn't like being charged when hot and will adjust accordingly. Has anyone else had something similar?

I highly recommend the Car Scanner app as it has key information when assessing a car. I'd bet you can can get a very good idea of battery health by looking at the individual cell voltages using this app.
 

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I too have wandered the web looking for a definitive statement but even though electric cars have been around a few years there is no simple explanation or plan. If you need only 80% then it would be better to only charge to that amount because they say the sweet spot for battery longevity is between 20-80% but if you need 100% because of a longer trip then what I have read is go to 100% but do not leave it sitting for longer than 8hrs fully charged. I wait till I am down around 20% then charge to 80%. If I am going a fair distance the next day I often Level 2 charge to 80% two days before then top it off to 100% using Level 1 the night before I leave - I am lucky I have both Level 1 and 2. If I don't drive a longer distance I still charge to 100% once a month but make sure I do not leave it at 100% - check out the Battery University online or this article is not bad, Battery charging: Full versus Partial - 🔋PushEVs BTW some people charge to 100% every night and have no concerns! Not exactly a black and white answer but most of the above appears in a fair number of places.
Looking at this 70% is by far the best level to charge to even if it means more frequent charging. 70/10 gives you the same range as 80/20 but almost 2x the charge cycles. This is assuming you don't have range anxiety. My average daily driving is 40 miles a day so I can easily 70/20. My home charger can add 10% per hour so if I'm going to need more range it doesn't take long to add it. Even running 70/0 is better than 80/20 so I'll bet it's better to charge to 70% and use a DC charger in a pinch if your caught short. My goal is for this to be the last car I own so I'm shooting for 375k on the battery. To those looking to get an ev it's really not a pain to maintain these battery levels and not something you need to think about if you have a lvl2 home charger. I set my car to 80 once and that's where it stops. When I get home if it's around 30% I plug it in which takes 2 seconds and unplug it next time I use it. With almost 300 miles of range charging to 80% gives you 200+ miles which is FAR more than the average person drives. Right now I'm charging every 4 to 5 days when I have 60miles of range left. My 1st week having the car I charged it up to 94% on the lvl1 it came with (ran out of time to charge) and drove 200 miles round trip with no stopping to drop a friend off at school. Whenni got home I still had over 70 miles of range and went about my daily business. When I got home that lvl1 charger said it was going to take 31 hours to charge. That night I bought a juicebox 40 which my state gave a $400 rebate for.
 
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