Customer Review

36 of 39 people found the following review helpful
4.0 out of 5 stars Charger works but..., April 15, 2011
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This review is from: Schumacher SC-600A-CA SpeedCharge 6 Amp High Frequency Battery Charger (Automotive)
This charger works fine but a "problem" a lot of battery chargers have is that they won't charge 12v batteries with a voltage less than about 7-9v. The reason for this is because if the charger is designed for 12v batteries only, they don't want you charging 6v batteries. Additionally, you usually can't charge batteries with a voltage of less than 2v because in order to protect the user, no power is applied unless a battery is connected and at such a low voltage, the charger thinks you have the wrong battery type or no battery there at all! There is a simple solution to this problem..

If you want to charge a battery that is at a very low voltage, as low as 0V, all you have to do is get another battery that DOES have a charge, get some jumper cables, and connect the Positive to positive and negative to negative. Then hook up the charger to the dead battery (positive to positive, negative to negative) and charge at the lowest rate for about 6 hours+. Periodically, (if in a bit of a hurry) stop charging, and disconnect the good battery and check the voltage of the battery to be charged. Once the voltage of the battery to be charged gets to about 10v, you'll no longer need to keep the "good" battery hooked up and you can continue to charge the discharged battery from now on.

Why does this work? It works because by hooking up a working battery to the discharged battery and then charging with the charger, the charger detects the good battery voltage and so will allow to charge. Only advice I have is during this setup, make sure the discharged battery, while it's charging does not "bulge" or do any other odd behavior. I've charged over 30 batteries like this and only one has started to "bulge" while charging and that was probably a bad battery anyway (shorted internally).
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Tracked by 1 customer

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Showing 1-3 of 3 posts in this discussion
Initial post: Jun 24, 2011 12:30:06 AM PDT
kalyson says:
Very helpful comment posted here.

In reply to an earlier post on Nov 10, 2012 11:16:48 AM PST
E. Snyder says:
I fear the good battery will pour many amps into the dead battery...I would remove the good battery ASAP (as soon as the charger will charge w/o it being there).

In reply to an earlier post on May 21, 2013 8:27:03 PM PDT
David says:
Yes it's true it will pour many amps into the dead battery but so long as the battery is discharged because of something like a parked car for 6 months with the computer draining it or something to that effect, and the battery doesn't have any faults of its own, it should be ok but it's important to be cautious in the event the battery is defective. The draw from the good to weak battery will be high initially but will slow as the battery voltages get closer to matching voltages. The vast majority of the battery's capacity is from 11v+ so 0-11V is only a small fraction of battery capacity so if there is a strong draw, it won't be for 20+ hours @ 2amps like it will take to fully charge a very discharged battery from 0v to 12.7V which is full charge.
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