Generally speaking, charging slowly rather than quick is better for battery health.
That said, i wouldn’t suggest charging while the battery is above, lets argue, 50%. Nor under 20%. Batteries degrade by charging/discharging fast, by being fully charged and by being very low.
If you can (and i understand that at 29 hours for a full charge that might not be possible all the time), i’d plug it in at 30%. If possible, you actually want to avoid charging to 100% as well. There’s no reason to do it (other than if you need maximum range of course). That’s a relic from times where batteries suffered from memory effect (reduced capacity if you didn’t charge them fully) – this isn’t the case with EV batteries.
This is was Kia says (matches what all other manufacturers say, just the first google result).
https://www.kia.com/dm/discover-kia/ask/how-to-extend-ev-battery-life.html
1. Minimize exposure to extremely high temperatures when parked
Exposure to the extreme heat while parking unplugged is when the frequent danger occurs. An automated temperature control system installed in your electric car will needlessly drain your batteries to keep the temperatures down for optimal efficiency. While this performance should only work when your electric vehicle is on the road using its battery, park your electric car in the shade or plug-in so that its thermal management system functions only using grid power, and make sure a stable range of temperatures during operation either.
2. Minimize the batteries at 100% state of charge
Electric cars already have installed with a battery management system that avoids them being charged and discharged at the extreme state of charge. Keeping the state of battery charge, from 0 percent to 100 percent , also improves the performance of the battery life of your vehicle. Even though a full charge will give you the maximum operating time, it is never a good idea for the overall lifespan of your battery.
3. Avoid using fast charging
If your batteries are soon-to-be die out, using a fast-charging is a great convenience. However, it presses so much current into the batteries in a short period which strains your EV battery and wanes them faster. While it is hard to notice its degradation, eight years of standard charging will give you 10% more battery life compared to 8 years of using fast charging.
4. Control the optimal battery state of charge during long storage
EVs that are parked or stored with an empty or full battery also degrades the battery. If you do not use your electric car often or having a long trip plan, get a timed charger, and plug it in. Leaving your vehicle at 100 percent while parked at a certain place for a long period, the battery will struggle with preserving its state of charge while you are away. One strategy is to set the charger to keep the charge just above the low mark, not filling it up to the maximum capacity, at an average charge level between 25 percent and 75 percent.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.