I have recovered several incorrectly charged (reverse-polarized) batteries by completely discharging them, and recharging slowly with the charger connected with the proper polarity, so don't make the blanket statement that it's impossible. That situation usually happens when the battery has been totally discharged by leaving headlights on all day, and some dummy connects a charger incorrectly when attempting to recharge it. If the battery is still in the car, it becomes very obvious that things aren't right because the alternator rectifier diodes burn out. If the battery is totally dead, and is removed from the vehicle for charging, it's possible to charge it with the poles reversed. The lifespan of the battery is shortened, but I haven't noticed any serious compromise of cranking amps, etc. once it is fully discharged and recharged with the right polarity. The process is similar to the procedure for breaking down a badly sulfated battery, where it is repeatedly discharged and re-charged, causing the crystalline lead sulfate to re-dissolve.
Anytime an automotive cranking battery is discharged below 75% of its full-charge capacity, it will have trouble recovering a complete charge. That is the main difference between cranking batteries and deep-cycle batteries intended for forklifts, power wheelchairs, trolling motors, etc. Those batteries can be discharged to 25% of their total capacity and recharged without damage, but they cannot provide the heavy surge of current necessary to run a starter motor. Cranking batteries are designed to provide a short surge of heavy current, and undergo a fairly quick recharge to full capacity. Deep-cycle batteries discharge more slowly, and require a relatively long, slow-rate recharge.
Jerry
Last edited by Hotrod Lincoln; 05/06/2011 1:24 PM.
