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Why does a matchbook sized cell phone battery require 3 hours to charge

Discussion in 'Electronic Basics' started by Ignoramus2168, Jul 2, 2007.

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  1. My Motorola cell phone has a matchbook sized cell phone battery. If it
    is discharged, it takes approximately 3 hours to charge from the AC

    My question is WTF.

    My 100 times bigger DeWalt battery can be charged in several times
    less time than that. Can't someone finally make a good AC wall

    Is there some device that I am missing. It is not rocket science.

  2. Tom Biasi

    Tom Biasi Guest

    The designer will have the battery charge according to its required
    Within these parameters there is a range of acceptable charge conditions.
    Power tool users want the unit in service ASAP so the charge is fast.
    Cell phone users usually want the battery to last as long as possible so the
    charge rate accommodates that.

    In short,
    Batteries have different chemical makeup and require different charging
    conditions. The manufacturers try to optimize the use of the product.
  3. Brent

    Brent Guest

    most cell chargers are designed for trickle charging to avoid heat
    buildup or to charge off the power provided by the USB bus of a

    Power tools arent as picky about contact with skin or heating the
    cells up (my hitachi lithium has a fan on the charger)

    I think part of the theory is to charge the cell while its user sleeps
    or it otherwise stationary whereas if youre charging a tool battery
    its genrally to use it
  4. Guest

    I suspect the ability to dissipate the heat generated by the charging
    current is the difference. Another difference is the chemistry in the
    two batteries. Your DeWalt is probably nicad while the cell phone is
    NMH, or perhaps some more exotic chemistry.

  5. Tom Gardner

    Tom Gardner Guest

    Get a DeWalt cell phone!
  6. b

    b Guest

    Your cell fone's battery is probably lithium-ion and it has strict charging
    requirements that are usually computer controlled. Your cell fone probably
    is the computer that is controlling its needs.

  7. Leon Fisk

    Leon Fisk Guest

    For the most part the faster you recharge a battery the
    shorter its life span. Three hours isn't all that bad though
    for a decent charge. They are probably trying to balance
    re-charge time with warranty expiration date.

    Their (Motorola) old two-way radio equipment from a few
    years ago use to take 12-16 hours with a "standard" charger.
    Go talk to any of your local police agencies and ask them
    about radio/phone batteries, cost, charging times, life
    expectancy... you'll surely get an earful that you won't
    soon forget :)
  8. Wild_Bill

    Wild_Bill Guest

    I haven't bothered to look into the numerous consumer alert-type stories
    that have been on the TV news, but there have been quite a few regarding
    laptop and cell phone batteries starting fires, sometimes in pockets,
    briefcases or luggage.

    It's been suggested/discussed here in RCM before, that in general, the best
    battery charging is slow charging.. both in terms of quality/level of
    battery output and long battery life.

    The instant gratification or demand for instantaneous results (commercial
    uses) of power tool, or critical use batteries have contributed to the
    availability of rapid-charging battery chemistry and construction design

    Forcing rapid chemical changes can't be good for long battery life, and
    probably reduces the useful charge output, in most cases (for most types of

    metalworking projects
  9. Eeyore

    Eeyore Guest

    The minimum time to recharge a battery is restricted by the charge rate it can

  10. JR North

    JR North Guest

    Tom routinely thinks outside the box. Classic example.
    Dweller in the cellar

    Home Page:
    If you're not the lead dog, the view never changes
    Doubt yourself, and the real world will eat you alive
    The world doesn't revolve around you, it revolves around me
    No skeletons in the closet; just decomposing corpses
  11. JR North

    JR North Guest

    My 2600 MAH AA Nimh cells fast charge in 3 hours, and get moderately
    warm doing so. As others have pointed out, heat dissipation is the key.
    Dweller in the cellar

    Home Page:
    If you're not the lead dog, the view never changes
    Doubt yourself, and the real world will eat you alive
    The world doesn't revolve around you, it revolves around me
    No skeletons in the closet; just decomposing corpses
  12. Your DeWalt battery gets very hot doesn't it. It is out in the
    air. The smaller battery that is inside a cover that might heat sink
    and might be even a heat source... Trickle current to slowly charge.

    One hint - 120v chargers put out 10% more than operating current.
    Turn off cell phone and then plug it in. Faster charge.

    Get a car unit - plug into the 12V socket - charges faster in any mode.
    Higher current available.

    I keep the car one in the car at all times. I can get it if I need it
    for use on the tractor or generator (power out).

    We charge at night - off and charge. Seems to work for us.

    I think the real trick for you is turning off the cell.


    Martin H. Eastburn
    @ home at Lions' Lair with our computer lionslair at consolidated dot net
    TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot's Medal.
    NRA Second Amendment Task Force Charter Founder
    IHMSA and NRA Metallic Silhouette maker & member.
  13. Eeyore

    Eeyore Guest

    Only 10% more ? You have to be joking.

  14. In my experience, at a 3-4 hour rate, the cells only noticeably warm up
    from getting fully charged and beginning to be overcharged. It appears to
    me that most "smart chargers" detect full charge by detecting directly or
    indirectly this temperature rise. What I suspect is an indirect detection
    of temperature rise is cell voltage decreasing after peaking from full
    charge. I suspect this is why "smart chargers" tend to work with shorter
    charging times of 4 hours or less.

    Meanwhile, there are some aggressive chargers out there, such as 30 and
    15 minute chargers for AA NiMH cells. 15 minute chargers require
    compatible cells of especially low resistance. I have a charger that
    actually charges 2,000 mAH AA cells in 15-18 minutes. It has a fan. The
    cells get fairly warm during charging, and are almost too hot to hold
    when they reach full charge.

    - Don Klipstein ()
  15. I had a rechargable battery explode in my hand. It unwound like a biscuit
    can, and startled me. Hot batteries apparently have a bit of pressure in
  16. John Husvar

    John Husvar Guest

    Most of the battery folks I deal with recommend a charge rate of 1/10
    the amp-hour capacity of the battery unless the battery is made
    specifically for fast charging. Fast recharge batteries get really warm
    toward the end of the charging cycle too.

    The new lithium-iron phosphate chemistry looks promising since it can
    handle the high discharge rates and has very good recharge rate,
    capacity and cycle rating. (one-third to one-fourth size for a given
    amp-hour capacity and recharge time of 1-1/2 to 2 hours for wheelchair
    service and ~5000 charge cycles, for example)

    Ya wanna see a lithium battery get hot? Short one. Wear safety
  17. Eeyore

    Eeyore Guest

    Cellphone batteries *are* designed for faster than 10 hour recharge though.

    That's not what the previous poster said anyway.

  18. Guest

    Most cell phones I've owned lately, have had optional "travel-
    chargers" available from the manufacturer, which charges the battery
    in about 1 hour. Also the phone controls the charging so that when the
    battery is fully charged, it will stop charging. So, I don't think
    that the long charge times are unavoidable due to the battery type
    itself. There has to be another explanation... maybe it's a marketing
    thing... include the "slow" charger with the phone and sell the faster
    one as an "option" for about $40 more.
  19. Martin sez:

    "> I think the real trick for you is turning off the cell".

    Right on Martin. It would be a real trick, and one he is incapable of.
    Iggy won't turn off any appliance he can bleat incessantly over and make a
    general nuisance out of himself.

    Bob Swinney
  20. craigm

    craigm Guest

    Try using google for answers. With very little efforts you can find this.

    or this
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