The situation you’re describing involves several factors related to how electric scooter batteries function, their state of charge, how battery indicators work, and the charging process. Let’s break it down:

1. Battery Voltage vs. State of Charge: Batteries, especially Lithium-ion (Li-ion) which is likely what you have, don’t discharge in a perfectly linear fashion. The relationship between voltage and state of charge is more complex. At the beginning and end of the discharge cycle, the voltage drops more steeply, while it remains relatively stable in the middle of the discharge cycle. Your scooter’s battery is rated at 36V, with a full charge voltage of 42V. When you see it dropping to 35V quickly, it may still be relatively high in terms of actual energy storage but is entering a range where the voltage begins to drop more noticeably with use.

2. Battery Indicator Inaccuracy: The battery bars on electric scooters (and many other devices) are not always an accurate representation of the actual battery capacity remaining. They are often calibrated in a way that the first and last bars disappear more quickly than the middle ones because they are trying to match the non-linear voltage drop. This can sometimes be misleading about the actual battery level.

3. Charging Time Consistency: The fact that it takes 8 hours to charge whether you’ve used one bar or all four doesn’t directly mesh with what one might expect, as charging typically is proportional to the deficit in battery capacity. This could be due to several reasons:

- Battery Management System (BMS): The BMS controls charging to protect the battery and ensure longevity. It might be programmed to slow charge as a default, regardless of the depletion level, to reduce stress on the battery, particularly during the final phase of charging where it balances the cells. This can make the charging process seem uniformly long.

- Charger Output: If your charger is limited in terms of amperage output, it may not deliver a fast charge at the beginning and then switch to a slower charge as the battery reaches full capacity. It’s designed to provide a constant, slower charge to promote battery health.

- Battery Condition: If the battery is aging or has some cells that are underperforming, the BMS may spend additional time trying to balance the cells, even if not much energy was used. This might not be noticeable in battery level indicators but could explain consistent charging times.

4. Voltage Drop to 35V: Dropping to 35V after using just one-fourth of the battery capacity could indicate an issue with the battery itself or how the scooter is calculating remaining battery life. It could be an indication that the battery is not holding charge as well as it should, which might be due to aging or damaged cells within the battery.

What to Do:

- Check the Battery: Have the battery checked by a professional or use a battery management tool if available to assess the health of the battery and ensure all cells are performing correctly.

- Review Charging Equipment: Ensure that your charger is the correct one recommended by the manufacturer and is functioning properly.

- Update Firmware: If your electric scooter supports firmware updates, ensure it’s up-to-date. Sometimes, battery management and monitoring algorithms can be improved through software updates.

- Battery Replacement: If the battery is older, has been heavily used, or shows signs of degraded performance (like not holding a full charge or significantly decreased range), it might be time to consider replacing it.

Understanding these factors can help you troubleshoot battery issues with your electric scooter or determine if professional service or further action is needed.를 한국어로 번역