Alternator & ChargingQuestionCommunity Starter

Question: Fast charging slows down earlier than it used to

TowTravelerCommunity StarterApr 7, 20262024 Rivian R1S Dual-MotorPortland
2024 Rivian R1S Dual-Motor, about 96,000 miles. On road trips the car used to hold a higher charge rate longer. Now it starts tapering sooner even when the pack is warm. Could this be charger-side variation, battery temperature, software, or an actual battery-health issue? I'm in Portland. If I fix it I'll come back and update the thread.
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14 replies

TowTravelerCommunity StarterCommunity StarterApr 7, 2026permalink
Tried a second charger / second scan and the story on the 2024 Rivian R1S didn't change. Parking it somewhere I can hear it better next time.
BoxerDadCommunity StarterCommunity StarterApr 7, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2024 Rivian R1S — site sharing and pack temp change the curve a lot. That's where I'd start. This is from a 2024 Rivian R1S in Portland with 96,000 miles. Any freeze-frame data saved? I already checked the easy fluid levels.
TruckOwner47Community StarterCommunity StarterApr 7, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2024 Rivian R1S so service can see what you saw. That's where I'd start. Keep sale price, fees, and rate as three different conversations. Parking it somewhere I can hear it better next time.
TruckOwner47Community StarterCommunity StarterApr 7, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2024 Rivian R1S so service can see what you saw. I'd do that before spending real money. Keep sale price, fees, and rate as three different conversations. Not driving it hard until I know more.
TowTravelerCommunity StarterCommunity StarterApr 7, 2026permalink
I went back under the 2024 Rivian R1S and it only happens after a heat soak, not on a cold start. I keep a notes app thread for this now.
TowTravelerCommunity StarterCommunity StarterApr 8, 2026permalink
It did fast charging slows down earlier than it twice this week, both times after sitting. No change in mileage feel. I'm keeping receipts and dates in one folder.
TrailTech93Community StarterCommunity StarterApr 8, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2024 Rivian R1S, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. Then you'll know the next fork. On “fast charging slows down earlier than it,” that was the fork that mattered for me. Do that first. This is the version I'd tell a friend.
TruckOwner47Community StarterCommunity StarterApr 9, 2026permalink
Not convinced that's the whole story. Try a second charger before blaming the 2024 Rivian R1S — site sharing and pack temp change the curve a lot. Then you'll know the next fork. This is from a 2024 Rivian R1S in Portland with 96,000 miles. Write the result down so the next test isn't a repeat of the last one. Only after sitting overnight so far.
BoxerDadCommunity StarterCommunity StarterApr 8, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2024 Rivian R1S — site sharing and pack temp change the curve a lot. That's where I'd start. Have you gotten a second quote in writing? I'll update if anything new shows up.
TrailTech93Community StarterCommunity StarterApr 8, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2024 Rivian R1S so service can see what you saw. Then you'll know the next fork. Stop there until you know. No warning lights, which is why I'm documenting it.
TruckOwner47Community StarterCommunity StarterApr 8, 2026permalink
Charge curves lie if you don't match starting SOC and temp. Match starting SOC and battery temp if you're comparing 2024 Rivian R1S charge sessions. That's where I'd start. This is from a 2024 Rivian R1S in Portland with 96,000 miles. Time, temperature, and whether it's in gear are the notes that actually help a shop. A day of patience here is cheaper than a wrong part. I'm in no rush to be a hero on it.
BoxerDadCommunity StarterCommunity StarterApr 8, 2026permalink
Charge curves lie if you don't match starting SOC and temp. Match starting SOC and battery temp if you're comparing 2024 Rivian R1S charge sessions. I'd do that before spending real money. When does it actually happen? I keep a notes app thread for this now.
BoxerDadCommunity StarterCommunity StarterApr 8, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2024 Rivian R1S, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. That's where I'd start. On “fast charging slows down earlier than it,” that was the fork that mattered for me. This is from a 2024 Rivian R1S in Portland with 96,000 miles. Was this after sitting overnight? This is me being the wet blanket on purpose.
BoxerDadCommunity StarterCommunity StarterApr 8, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2024 Rivian R1S, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. Then you'll know the next fork. On “fast charging slows down earlier than it,” that was the fork that mattered for me. Have you gotten a second quote in writing? If your situation is the opposite, ignore me. I'd rather look cautious in this thread than stuck later.
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