I considered calling this piece “I’ve been charging my batteries wrong and four other facts about battery chargers.” In fact, a lot of this is going to come off as common sense for those who have taken the time to read the manual for their battery charger. That’s because it comes to us not only via advice from our friends at Clore Automotive, but simply by virtue of a close reading of both the manuals for their “CHARGE IT!” line of portable and wheeled chargers, which have information specifically targeted at older exotic and classic cars and tractors, and a review of the instructions for my own DieHard charger, a circa-2010 legacy of my father, which seems to no longer be in production. They’re interesting and useful tidbits that may have eluded those of us who learned how to charge a battery via instruction or intuition.
1. There’s a reason for the range of amp-selection choices
Your charger, like mine, probably has several different settings to choose from. As seen below, mine has 2A, to use for smaller batteries, like those used in motorcycles and lawn tractors, and in certain other instances; 12A, “Fast Charge” for automobile starting batteries and marine/deep-cycle being charged with no special urgency; 30A, “Rapid Charge” for attempting to get a car or boat started in a hurry; and an 80A “Starting Mode” designed to work as a stand-in for another car when jump starting. I used the latter a couple times driving my ’64 Rambler through the subzero Michigan winter of 2013-’14 and I can vouch for its efficacy. The Charge It devices have similar settings: 10A for charging deep-cycle batteries, 40A for “Maintenance-free Automotive or Marine Cranking” units, plus a “high-amperage” starting mode.
2. Desulfation increases battery life
Other chargers I’ve had in the past had indicators for a special “Desulfation Mode” and while this one doesn’t, it does boast a secret blinky code disclosing that it has entered desulfation (a process that can last up to 10 hours!). What is sulfation, you might ask, and why must we reverse it? Sulfation occurs as a natural process of the battery’s chemical reactions. As the battery discharges, the sulfur derived from the sulfuric-acid electrolyte binds to the lead plates. This is normally reversed during charging, but chronic under-charging (often a result of lots of short trips) or long-term discharge (i.e. the car wouldn’t start and you just left it to sit after running down the battery) can result in that bond becoming semi-permanent.
Reversing the process comes from a kind of controlled overcharging that is only possible for hobbyists like me thanks to modern microprocessor-controlled battery chargers. You can see why in the 1920s, battery service stations were very much a thing: the sulfuric acid inside the case, the hydrogen gas produced during charging (still a risk—so watch out for sparks) and the serious electrical equipment involved made it a far more complicated hazardous undertaking back then.
3. Don’t fear positive-ground systems
Both my charger and the Charge It happily accommodate six-volt batteries. Charge one in the car and it’s good practice to double check which way the car is grounded. All modern cars and most older cars use the seemingly intuitive negative-ground system, where you’ll find the battery grounded to some heavy part of the chassis via its negative post. The opposite, called a positive-ground (“positive-earth” in other parts of the world) system, has some theoretical advantages, however, and is relatively common in the old-car scene—even on some 12-volt vehicles. The Charge It manual says the positive-ground arrangement “is usually found in pre-1970 foreign vehicles or pre-1970 farm tractors,” to which I’ll add many pre-1956 American automobiles.
Should you find yourself charging a positive-ground car (or farm tractor), you’ll simply need to reverse usual practice: connect the negative cable to the battery’s negative post and the positive cable to some sturdy chunk of metal at the other side of the engine compartment (NOT fuel line, carburetor, sheetmetal, etc.). Charging on the bench is even easier: just hook the battery up as shown in section 5.