27++ battery discharge pattern

[Chatbox]

So, I have two batteries.  55++ and the 27++.  Both are 9cells each, and with a designed capacity of 93.24Wh.

The dischrge pattern between the batteries while they're both hocked up to the W520 is that the 27++ will first get dischange...all the way down to 0%, then and only then will the 55++ start to discharge.

This is potentially damaning to the 27++ in terms of faster wear, and long term battery health.

Is there a way to configure the system to switch over and use the 55++ battery once the 27++ drops down to a particular level, say, 25%.  ...without manually disconnecting the 27++?

[harrisb]

The slice battery is protected from total discharge.The system will switch over to the internal battery when the microprocessor on the slice battery signals that it is at 0%. The microprocessor will protect the battery from further discharge when that power state is reached.

[Chatbox]

So even when the slice is reporting 0%, it in fact is not the cells' 0%?  Am I understanding correctly?

Does this logic also apply to the 55++?

[harrisb]

Yes, the 0% is not the cell discharge level, but the 0% of power that can be safely drawn from the battery. All Li-on batteries from Lenovo have the builtin microprocessor that protects the cells.

[ColonelONeill]

While the cells will still have charge at "0%", the closer to the reported 0% you drain, the faster the battery wears out. The declared 0% is simply the somewhat arbitrarily determined threshold set in the controller.

[harrisb · Accepted solution]

The behavior is normal. There are no settings in the power manger to change the switchover %

[Chatbox]

I wonder if there's a way to submit a feature request to Lenovo...

Or maybe they just want the batteries to wear out quicker...so they can sell more.