Should my tablet battery drain completely before recharging?

Discussion in 'Hardware' started by Ramrock, Feb 10, 2012.

  1. Ramrock

    Ramrock Pen Pal - Newbie

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    I habitually allow my batteries (slate, laptop) to drain almost completely (to 8 or 7%) before connecting to power source. I usually don't connect to power source until the battery is that low, even if an AC source is available. On the other hand a friend uses external AC power exclusively, depending on battery only in the absence of an external power source.

    Is it ok to work with AC power even when the pc battery is fully charged without damaging the battery? Or must I drain the battery each time before connecting to external power source?
  2. Hattori Hanzo

    Hattori Hanzo Scribbler - Standard Member

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    Short answer: yes.

    Modern batteries feature controller chips that are above your average desktop calculator to make sure batteries don't get over charged or drained to the point of being damaged.

    Long answer:
    Practically Li-<something> batteries die over time no matter what you do, but the process is dependent on temperature and charge level. The fuller and warmer, the faster they die.
    So leaving them while working on AC indeed shortens their lifetime if it's the common usage scenario. They get warmed through the heat from the laptop and are usually full rather soon.
    That's not a problem for some hours, but if they work like that most of the time it's bad. Think of the typical office worker who only takes his laptop off the dock twice a week for a one hour meeting, he has a problem.

    Another thing about discharge levels is that Li-Ion batteries like full cycles less than partly cycles. So if you can choose between half draining and loading and full draining and loading, choose to only half drain the battery, unless this means adding an additional cycle.
    E.g. if you get home with a half full battery and have to load it for the next day, use AC immediately instead of waiting until you have just some percent left.
    From time to time a complete cycle is helpful to keep the battery meter accurate, though. It predicts the charge level based on some parameters that change when the battery ages. If the battery never gets drained completely, the battery controller has to guesstimate those changes and experience shows it gets off usually.

    So, whatever you do, your battery is going to degrade and eventually die. You have to trade off faster degradation and usage. Where and to what extent you do that is up to you.
    For the systems I regularly use I basically don't care much. If I keep my spare batteries on a low charge level, they're useless, so they are stored being fully loaded and die faster because of that. Only exception is one battery for a laptop that does not leave its dock anymore. That one's halfway charged and in the fridge, in a plastic bag, to keep it as fresh as possible until I need to use it.
  3. Steve S

    Steve S Pen Pro - Senior Member Super Moderator

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    <<...Is it ok to work with AC power even when the pc battery is fully charged without damaging the battery?..>>

    Ram: See this web page to learn a bit more about lithium batteries and their characteristics:

    How to Prolong Lithium-based Batteries - Battery University

    Like Hattori, I suggest that you use your battery routinely and not operate solely on AC power for long periods of time. That will shorten the life of your battery by a significant amount...

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