With modern Lithium ion batteries its because as their capacity decreases over time the BMS can’t always keep up and recover the 100% point unless you’re occasionally draining it all the way. This can result in someone charging their battery to say 97% and leaving it for hours to reach a 100% it will never reach. This is potentially unsafe as it heats up the battery.
This is correct with unmanaged batteries. Batteries with a BMS however will never get below whatever voltage is set as their 0% unless allowed to sit at 0% for long enough that e n t r o p y occurs and the charge slowly dissipates over time. This will happen even with a fully charged battery left to its own devices (ba dum tss) for too long.
The point of the BMS is to manage the health of the potentially dangerous lithium batteries, and as long as they are used within spec it should keep voltages from getting so low the batteries enter a state of deep discharge, as well as prevent overcharging due to imbalanced charging rates or other similar issues.
Used is the important word here. A battery must be used to maintain it’s health. A battery must also not be abused to maintain its health.
Now none of that touches on what you said, but was important background for this to make sense: The BMS will report to you whatever values it deems safe charging and Discharging limits based on factors like internal resistance and temperature. As a result 20-80% of an unmanaged battery is close to 0-100% of a managed one in new condition because the BMS will cut power before unsafe discharge limits are reached, and will stop charging to prevent overcharge once those limits are reached.
With modern Lithium ion batteries its because as their capacity decreases over time the BMS can’t always keep up and recover the 100% point unless you’re occasionally draining it all the way. This can result in someone charging their battery to say 97% and leaving it for hours to reach a 100% it will never reach. This is potentially unsafe as it heats up the battery.
Edit: Autocorrupt beansed up my comment
I was always told to always leave it charged from 20% to 80% and draining it to 0% was a bad thing.
This is correct with unmanaged batteries. Batteries with a BMS however will never get below whatever voltage is set as their 0% unless allowed to sit at 0% for long enough that e n t r o p y occurs and the charge slowly dissipates over time. This will happen even with a fully charged battery left to its own devices (ba dum tss) for too long.
The point of the BMS is to manage the health of the potentially dangerous lithium batteries, and as long as they are used within spec it should keep voltages from getting so low the batteries enter a state of deep discharge, as well as prevent overcharging due to imbalanced charging rates or other similar issues.
Used is the important word here. A battery must be used to maintain it’s health. A battery must also not be abused to maintain its health.
Now none of that touches on what you said, but was important background for this to make sense: The BMS will report to you whatever values it deems safe charging and Discharging limits based on factors like internal resistance and temperature. As a result 20-80% of an unmanaged battery is close to 0-100% of a managed one in new condition because the BMS will cut power before unsafe discharge limits are reached, and will stop charging to prevent overcharge once those limits are reached.