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Thread: Increasing lower discharge threshold of ultrabay battery before switching Lenovo T43s

  1. #1
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    Increasing lower discharge threshold of ultrabay battery before switching Lenovo T43s

    Sorry for the long title. I have a Lenovo Thinkpad T430s with an Ultrabay battery and a main one. When I plug in the two batteries, it will start draining my Ultrabay battery until it drops all the way down to 0% until switching to the main battery. However, I want to keep the discharge within reasonable limits - 10~15% of capacity - before switching to the main battery. I want to enjoy more capacity without having to physically remove my ultrabay battery in order to preserve it.



    According to http://www.thinkwiki.org/wiki/Tp_sma...pecific_status, Ivy bridge Lenovo do not support tp_smapi which is used to implement a script called tp-bat-balance (http://www.thinkwiki.org/wiki/Talk:Code/tp-bat-balance) that balances the usage of both batteries. I have installed tlp from http://linrunner.de, which allows some tweaking to the minimum and maximum charging thresholds, but not to the min discharging thresholds for the ultrabay battery.



    Has anyone found a workaround this?
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  2. #2
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    Re: Increasing lower discharge threshold of ultrabay battery before switching Lenovo

    I have a T43p with an Ultrabay. I think it is hardwired in BIOS. Perhaps look for a BIOS upgrade to see if there are any switches inside the BIOS. I think the current settings are fine when the batteries are new, but when the batteries get old, the hand-off can be risky. IBM/Lenovo's solution is to buy new batteries. The battery's charge and monitoring circuitry is quite sophisticated, but if one cell has started to degrade, the entire battery pack becomes a liability for your data.

    You could write a script using notify-send to check the battery level (every 10 minutes) and give more advanced warnings at 20% so you can save your work and prepare for the switchover. Then use acpitool to eject the Ultrabay device at 15%. I would try this a few times to make sure that the handover is clean.

    Code:
    man acpitool
    Last edited by tgalati4; February 14th, 2014 at 04:25 PM.
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  3. #3
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    Re: Increasing lower discharge threshold of ultrabay battery before switching Lenovo

    I still have to try it, but I don't think there is a problem with the switchover. When depleted the ultrabay, the laptop just starts consuming the main battery. Problem is only the 0% discharge that will suck the life out of the cells in no time.



    I will check on BIOS updates.
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  4. #4
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    Re: Increasing lower discharge threshold of ultrabay battery before switching Lenovo

    Hi,

    the behaviour of discharging the ultrabay battery first and down to 0% is a well known and often critizised ThinkPad feature. Afaik the only way to change this is to use some kind of balancing script.

    You'll have to use tpacpi-bat to achieve this because the T430s (as all ThinkPads of the Sandy Bridge generation and newer) is not supported by tp-smapi. You may use the version integrated into TLP: /usr/lib/tlp-pm/tpacpi-bat.



    Btw: TLP does not provide such a feature intentionally.

  5. #5
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    Re: Increasing lower discharge threshold of ultrabay battery before switching Lenovo

    The on-board battery charge and discharge circuitry protects the cells. So although 0% seems like sucking the battery dry, if you measure the voltage at 0% you will find that it is within acceptable limits for lithium ion cells. The real issue is when the cells are a few years old, the 0% gets crossed very quickly into a low-voltage/high-current situation. That will cause an immediate current overload fault and shutdown--possibly losing your work or not handing off properly to the main battery. You only get ~300 charge-discharge cycles so when you go from 100% to 0% or 80% to 20%, you might increase the cycles by a few percent, but you decrease the running time by a lot. It's a tradeoff.
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