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Extending the Life of a Rechargable Battery

Discussion in 'Electronic Design' started by [email protected], Oct 10, 2005.

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  1. Guest

    Ive heard its better for the life of a battery to charge a battery to
    full capacity, use it until it drains completely and then fully
    recharge it and so on. I heard the battery will go bad faster if you
    partially charge, discharge more frequently. Is this true? Does it
    depend on the type of rechargable battery?
  2. Jim Thompson

    Jim Thompson Guest

    NiCad are worst for that. Most other types aren't so sedative to
    discharge depth.

    ...Jim Thompson
  3. Joerg

    Joerg Guest

    Hello Jim,
    Yes, but AFAIK NiCd are the only ones that can be trickle charged. NiMH
    supposedly doesn't like that, making stand-by applications rather
    cumbersome (meaning more $$$) in terms of charger circuitry.

    Regards, Joerg
  4. A discharged battery has the potential to grow dendrites (whiskers) between the plates. Some formulas are better than others, Lead
    acid and NICAD are at the top of the list.
    Shocking Nicads tend to burn off the dendrites, but they eventually grow back.

  5. kell

    kell Guest

    for some batteries, yes. Just don't drain a lead acid battery. Bad
    for it.
  6. Robert Baer

    Robert Baer Guest

    *NO* battery "likes" to be fully discharged!
    That being said, the NiCd cells have a "memory" problem, and the only
    way to "reset" that is to do an almost complete discharge and then
    charge; sometimes this is needed moer than once for recovery.
    So, this regimen to "reset" their memory theoretically reduces their
    lifetime - but without the "reset" they are useless anyway, making the
    theory un-proveable and moot.
    Other uses that can shorten cell lifetime is heavy discharge and
    heavy, un-controlled charging.
    Roughly, a cell should not be discharged to less than 80 percent of
    rating, and the discharge rate should not be greater than C/2 or only
    "bursts" of C *if* the chemistry supports that.
  7. Not true. NiCds and NiMH batteries can be fully discharged, but not below 0V
    on any cell. A multi-cell NiCd battery may reverse charge a weak cell which
    *will* kill it. NiCds should be stored discharged (but self-discharge is good

    OTOH, lead-acid batteries must never be fully discharged. Deep discharging
    them tends to warp the plates causing shorts. "Marine" batteries have thicker
    plates (thus lower power-density and higher internal resistance) and are less
    susceptible to plate warping.
    The "memory" problem isn't. It's much legend about a totally different issue
    (one that has been pretty much non-existent for 20 years).
    Over-charging and reverse charge during discharge are by far the most common
    cause of early failure of NiCds.
    Not less than 80% of rating? Nonsense. Lead-acids shouldn't be discharged
    below 20%, perhaps. NiCds can be run to down to zero as long as the cells
    don't reverse polarity.

    You'd better talk to model airplane nuts and electric drill manufacturers about
    your C/2 or C "rule".
  8. Rich Grise

    Rich Grise Guest

    I "resurrected" a NiCd pack in a wireless phone once - it wasn't holding
    a charge, like I'd get two minutes of talk time, it'd beep, and go dead.
    Really pissed off one of my clients when the phone went dead on him.

    So I took the battery out, poked a 1K resistor into the connector, and
    let it discharge to approx. 0. Stuck it back in the phone, let it charge
    for a day, and it worked like new.

    I don't recommend this unless you're prepared to spring for a new
    battery if you actually kill it. :)

    Good Luck!
  9. ehsjr

    ehsjr Guest

    Not a pack, just an individual cell. The *proper* discharge
    level - the level at which the cells should be considered
    completely discharged - is about .9v per cell. With a single
    cell there is no risk of cell reversal, but with a pack,
    discharge should be limited to that .9v per cell level.

    Lead-acid 12V wet cell batteries should never be discharged
    below 10.5 volts.

  10. No, that's the "proper" voltage for a multi-cell application. A
    single NiCd cell can "properly" be discharged down to 0V. There
    isn't much charge under .8V or so though. Reverse charge is the
    worry here (which cannot happen with a single cell).
    That depends on the design. "Deep cycle" or "marine" batteries are
    better at this than "starter" batteries because of their mechanical
  11. I read in that Keith Williams <>
    The electrolyte concentration is different as well.
  12. ehsjr

    ehsjr Guest

    You are agreeing with what I wrote. Why the word "No" at the
    start of your sentence?

    That's what I said. "Not a pack, just an individual cell"
    which refers to your statement "NiCds can be run down to

    That's what I said. "With a single cell there is no risk of
    reversal, but with a pack, discharge should be limited to
    that .9V per cell level."
    No - finally we disagree! Regardless of design, discharging
    a wet cell 12V battery below 10.5 is a no-no. That includes
    deep-cycle/marine batteries. The open circuit voltage swing
    from 100% charged to 100% discharged is only about 2 volts.
    These batteries are 100% discharged when they reach 1.75
    volts per cell (10.5 across the battery), per the site above.
    Exide specifies a higher voltage: their FAQ says the battery is
    100% discharged at 11.7 volts

    This site lists ~11.8 volts as 100% discharged:

    This site shows 11.5 volts as 100% discharged:

    Even if you do not go below 10.5 volts, removing most
    or all of the charge (and by that I mean I mean lowering
    the state of charge such that the battery voltage approaches
    10.5 volts) reduces the battery life. For exmple, one
    of the sites mentions indicates that you'll get more than
    double the number of charge-discharge cycles from a deep
    cycle battery if you keep the discharge level to no more
    than 50% than if you keep it to no more than 80%.

  13. Phil Allison

    Phil Allison Guest


    ** A requirement that is practically impossible to comply with for packs of
    more than about 4 cells.

    Eg. A a 6 cell ( nominal 7.2 volt) Ni-Cd pack where all cells are

    Freshly charged = 9.0 volts.

    On load = 7.5 volts ( at half capacity)

    End point = 6.0 volts.

    Load cut off = 5.4 volts ( using the 0.9 volt per cell criterion )

    However -

    In the real world, one cell will always be weakest, reach end point first
    then go very rapidly to zero.

    The pack will still deliver 5 x 1.25 = 6.25 volts with one cell at 0

    So, the weakling can be reversed to -0. 85 volts before the 5.4 volt load
    cut out operates.

    With more than 6 cells, the situation gets worse.

    ........ Phil
  14. ehsjr

    ehsjr Guest

    Yup. When the pack ages to the point where one of the batteries
    is weak enough for the described scenario to occur, it is time
    to replace or repair it - or live with shorter times between
    recharge/lower power.

  15. Phil Allison

    Phil Allison Guest


    ** That is NOT what I wrote and not what was being demonstrated.

    Clearly you don't want to know the facts.

    ............ Phil.
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