Flooded cell lead-acid battery 101 (all I know, won't take long):

Your battery is basically lead plates (Pb) and sulfuric acid (H2SO4) when charged.

As it discharges, the sulfur in the acid moves to the lead plates, forming lead-sulfate (PbSO4) and water (H2O) (theoretical fully-discharged).

The lead-sulfate is not stable, it tends to sluff off of the plates to the bottom of the cells slowly during battery use if not converted back into lead. This will eventually lead to increased self-discharge from the lead sulfate in the bottom of the cells (short if it gets bad enough to connect the plates). Lead sulfate remaining on the plates will reduce the area available for chemical reaction which will reduce the available current (cranking amps), and the reduced plate mass will also lead to less battery capacity (amp-hours).

This can be converted back into lead and acid, to some degree. The common de-sulfating method is a charge voltage (IIRC) of 15.1vdc, often pulsed to reduce the heat buildup that can warp plates and cause irreversible damage via plates shorting/touching. Proper charging will also help to reduce dendrite buildup, which you can picture as little stalactites growing into the insulating layers between the plate layers, which can eventually cause shorts.

In automotive starting batteries the plates are usually designed thinner, with less mass, less space between them, and are optimized for surface area. They are designed to offer lots of cranking amps for a short time, and most of the time remain fully charged. Deep-cycle batteries often have thicker plates with more fiber reinforcement and deeper wells below the plates, this allows for heavier charge-discharge cycles to not heat-warp the plates, and the fiberglass reinforcement helps to hold the lead-sulfate together as the battery is designed to be operated with much of the lead converted to lead-sulfate. A normal car battery is not designed to take vibration etc. when discharged because the lead-sulfate will more easily sluff off of the plates and settle to the bottom.

Many large battery installations have de-sulfating cycles, my charger/inverter systems on my coaches always do, this is because the batteries are designed for this high-voltage charge without damage, and to outgas heavily during this cycle. Car batteries are not.

You can buy a de-sulfator I guess, but don't expect it to do a lot. You might be able to boil the sulfate off of the surface if you have a de-sulfator with enough current to maintain the necessary 15.1vdc regulated for the pulses. You will likely need to add water after this cycle, it should actively boil the acid and will create lots of corrosive (and explosive) gas.

Much MUCH more important is to properly charge the battery in service to a proper (14.3 bulk -> 13.4 float) operating voltage and avoid creating the sulfated condition. This is one of the complaints I have with these 1980s charging systems, even when my '91 was new you could watch the voltage drop every time you came to a stop with the lights and A/C on, constantly cycling the battery and not really fully charging until you get a long run without stops (which some cars never get). If this is your car, ... upgrade your alternator.

On these old cars there are very few parasitic loads (with the key shut off). My '87 will sit for a month or more in the winter when the roads are salted between starts. When I'm ready to start, turn the key and she lights right off. My new car OTOH cautions against parking the car for more than 2weeks without a battery maintainer. Unless you've added an aftermarket stereo with amps and stuff that draws a lot, you should be fine. You are much better off using no charger and checking your battery periodically than connecting a cheap charger (one without proper regulation, a "smart" charger). A charger without smart regulation will constantly overcharge your battery and it will outgas (corroding all around it) and consume water. I did have a trick years ago for a cheap charger, where I put it on a timer, ... only powering on the charger for an hour each night around 2am (RV parked outside in Michigan). This kept the batteries charged without overcharging, did it at the coldest time of night when they need the most protection from freezing.

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Gone to the dark side

- Jeff