Battery Health vs Usage Time

Discussion in 'MacBook Pro' started by ks-man, Jan 5, 2008.

  1. ks-man macrumors 6502a

    Joined:
    Sep 25, 2007
    #1
    Planning on buying a MBP soon...

    I've read a bit around here about battery health. I was wondering how the health of the battery relates to the amount of time the battery will work for.

    Is it simple arithmetic?
    Max battery usage is 4 hours (just picking a number) so if your battery health is at 75% will it last for 3 hours and if at 50% it will last for two hours?

    It seems that people get very concerned that their battery life dropped to 92-96% after 6-12 months, so that leads me to believe that the drop off in usage time may be more drastic. I would assume that after a year a battery lasting for over 90% of its initial full amount (in my example 92% of 4 hours would be 3 hours and 41 minutes) is still very good. This makes me wonder if a 90% battery health will only get you 50% of the original charge.

    Also when do people typically buy a new battery? When battery health gets under 90%, 75%, 50%???

    Thanks for the help. I'm just trying to get an idea of what I can expect when I get the MBP. I don't think it is unreasonable to have to spend $130 for a new battery after 18-24 months of use if I want to match the original full charge usage time. I'm wondering if people here start freaking out once their battery health goes under 98-100% despite the fact that it is a pretty minor deal in terms of how it will affect the real world performance.

    Thanks again.
     
  2. Techguy172 macrumors 68000

    Joined:
    Feb 2, 2007
    Location:
    Ontario Canada
    #2
    When the battery health drops it doesn't make much of a difference when it only drops 5-10% You may loose say 15-20 minutes off your battery. Now if it drops a lot then you will loose more Say it lost 50% then you will lose a little more than half your battery life.

    I would buy a new battery at probably 75%. How long your battery lasts is all up top your usage patterns and how often you charge and discharge. So if you use it very little then it will last a long time if you use a lot it won't last as long. Although if you barely use it will die rapidly. It's just the way lithium batteries work.

    Hope that helped!
     
  3. ks-man thread starter macrumors 6502a

    Joined:
    Sep 25, 2007
    #3
    It did, thanks. While not an exact formula it does sound like a 10% loss in battery health will cost you 10% of usage time (far from a tragedy after 6-12 months).

    Also when people say they've had 100 cycles, how is that measured? Is that anytime you unplug the laptop and then it recharges to full, or is that only for a full discharge and charge?

    If you unplug your laptop every day and use it for 30 mins and then recharge it to full, after a year would you have 365 cycles?

    Thanks.
     
  4. MarkMS macrumors 6502a

    Joined:
    Aug 30, 2006
    #4
    I was going to post in my own words, but I think this page from Apple will help you.

    FROM APPLE.COM/BATTERIES
     

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