20amp 12v lead acid battery overcharging ?

Discussion in 'Power Electronics' started by MeGuinness, Mar 17, 2015.

  1. MeGuinness

    Thread Starter New Member

    Mar 17, 2015
    hello, wondering if you guys can help me,
    i have a 2x identical 12v 20amp lead acid batteries , one of them due to been left in the garage unattended for about 2 years had a voltage output of about 1V ,i know practically dead,anyway in trying to salvage it before go and buy a new one i decided to top it up with some deionised water and put it on charge using a RC charger in Pb mode .
    Due to the low voltage the charger would not start the charge.
    After some thinking ....I connected the good and the dead battery together in series and left them for one hour.. .....once I removed the connections the dead battery voltage was up to about 12.40V ,so I quickly connected the charger and yes it started charging no problem. I put the settings at 0.5amp charging .

    Now the fist battery was still at 12v and using the same charger i had no problem in fully charge it ,the charger did put about 6000mah and stopped when it was time to.

    My problem is with the second so called dead battery ,yes i managed to start the charge but the charger will not stop charging even after putting in about 28000mah in it and a voltage of 13,20V.
    If the battery is rated at 20amp how is that the battery could take 28000mah??? what is wrong ?is it overcharging ?
    i left the battery off the charger for a day and when i checked the voltage is at 12.46V .
    Any ideas ?thanx
    [​IMG] [​IMG]
  2. tcmtech

    Distinguished Member

    Nov 4, 2013
    First off recharging a battery is not the same as charging up a capacitor so be expecting considerable ah discrepancies between the batteries AH rating and how many AH go into recharging it.

    Basically regenerating a near flat dead battery takes a lot more charge than just what its AH rating is.

    Personally if it was me when I try to regenerate dead batteries I try to hold them at around 14.4 volts give or take a few 10ths for a good day or two before concerning myself with what their amp draw is or what their voltage stays at.
  3. Lumenosity


    Mar 1, 2017
    Old thread....but still a good one.....for the benefit of others who find this thread....

    Also, remember that a battery's capacity is a much better indicator of it's condition than it's voltage.
    You can buy a 12v battery that is nearly the size of a AA battery.....but do you think that will start your car? Why not?
    It's also 12 volts...... The answer is capacity. Technically the ability of the battery to hold electrons on it's plates and move them across the plates.

    So a car battery might charge to 13.3 Volts ....but have the capacity of a VERY small battery because the plates inside no longer have the ability to hold and transfer electrons (or very few relatively speaking).

    In addition to what tcmtech said, I use 20watt 12v solar panels on larger batteries and 10watt, 12v solar panels on sulfated smaller batteries.
    The solar panels peak at around 20v in the brightest sunlight but it "pulses" somewhat as clouds pass. I've rejuvenated quite a few batteries this way. But I think it's a matter of expectations. If you expect to rejuvenate a 5 year old battery to near full capacity you are going to be disappointed. I have 80AH batteries that finally went flat with only 1Ah capacity remaining and have brought them back up to 20-30Ah with Solar panel desulfation. Plenty good enough for battery backups and a few other similar purposes.

    But eventually a battery will become so damaged inside that nothing can bring it back to life for any intent of useful purpose.
  4. marcf


    Dec 29, 2014