How to Recondition a Car Battery?

Most cars still use lead-acid batteries of some kind - wet/flooded, AGM or even Gel-cells, but these batteries over time lose their capacity and the ability to start the engine.

Since quality car batteries are not cheap, many people wonder how they can recondition a car battery at home. Reconditioning car batteries at home can be done successfully, but this also depends on the battery type, its use, age, current condition and similar.

Updated: January 14, 2022.

Lead-Acid Batteries 101

For short, lead acid batteries consists of positive and negative lead plates and diluted sulfuric acid as electrolyte.

Lead plates are sometimes made of pure lead, sometimes with added calcium and other alloying elements in order to achieve certain goals, like stiffer plates, lower self-discharge rate, etc.

Chemistry: Charging and discharging process is reversible and includes creation of Pb and PbO₂ (charging) and PbSO₄ (discharging) on the battery plates (very simplified) - in the fully charged battery, the negative plate consists of Pb (lead), and the positive plate is PbO₂ (lead dioxide).

However, charging/discharging cycles are not perfect - with each cycle, newly created Pb, PbO₄ and PbSO₄ are not formed in the 'exact' proper way as before.

Also, lead–acid batteries lose the ability to accept a charge when discharged for too long due to crystallization of PbSO₄ (also known as sulfation process).

There are other processes that over time, little by little decrease the battery's capacity and its ability to provide large currents.

Types: Most common lead acid battery types are wet/flooded, AGM (Absorbent Glass Mat) and Gel-Cell batteries.

Wet/flooded batteries have their electrolyte in liquid form, hence the name. Over time, water from the battery is lost and must be added in the form of distilled water - never add a tap water into the wet/flooded battery.

AGM and Gel-Cell batteries are Sealed Lead Acid (SLA) batteries and there is nothing what common user can do regarding the electrolyte - there is no need (and no option to do so) to add water during the operating life of the battery.

Reconditioning Car Batteries at Home - Recommended or Not?

Well, there are several ways to recondition a car battery at home.

One of the 'most famous' methods which is applicable ONLY to wet/flooded batteries include removing sulfuric acid from the battery, cleaning the cells with baking soda and then adding custom electrolyte based on the Epsom salt (magnesium sulfate) and distilled water.

To do this at home, one requires open area (it should not be done inside, no matter 'how well' the area is ventilated!!!), protective gear (gloves, goggles, etc), chemicals etc.

But, personally, it is not recommended for many reasons:

- these chemicals (sulfuric acid!!!) are dangerous, even fumes and invisible droplets!

- battery must be in working order (preferably above 12 volts) to achieve 'some' improvement.

- battery cannot be made 'as good as new', especially if it was discharged (almost) fully.

- modern batteries feature lead plates that are quite thin, much thinner than the batteries' plates few decades ago - if the plates are twisted and there is a cell with a short circuit, that battery is dead and should be recycled.

For short: not recommended, to say the least!

However, there is a much simpler and much safer method of reconditioning a car batteries at home, regardless of the type (wet/flooded, AGM, Gel-Cell) and charge/discharge level (even if the battery is fully discharged, down to the cell reversal) etc. - get a smart lead-acid car battery charger. It is that simple.

Features and Specifications of Smart Lead-Acid Battery Chargers

Smart lead-acid battery chargers are microprocessor controlled devices that analyze the battery condition and charge it according to:

- battery type: user usually have to set the battery type commonly including wet/flooded, AGM, Gel-Cell, Calcium, Lithium etc. Since all these batteries have somewhat different charging characteristics (especially if the lithium batteries are supported/charged), setting exact battery type help the charger adjust charging voltage/currents according to the battery in question.

Note: Never, but really never charge lithium batteries with charges not designed for such batteries ...

- battery use: according to the battery's use, set this to either float or cycle use (if available on the charger, of course).

- temperature: some battery chargers feature temperature probe that measures temperature of the battery, allowing the charger to adjust the charging voltage according to the temperature. This prevents overcharging and undercharging of the batteries.

If you have wet/flooded battery, be sure to check electrolyte level prior charging and if required, add some distilled water. Also, check maximum allowed charging current of your battery and be sure to use battery charger that features maximum charging current lower than the battery's maximum allowed charging current - charging the battery with too strong currents may destroy it easily, especially AGM and Gel-cell batteries.

When charging process starts, smart battery chargers analyze the battery and start with the recovery/charging (depending on the settings/model of the smart battery charger):

- charge/recover dead battery: if the extra low voltage is detected (for example, below 6 volts, even down to 1 volt!), battery charger may start with the desulfation of battery plates, slowly increasing battery voltage. 

Note: some battery chargers even feature 'Force Mode' allowing the user to override microprocessor and to 'force' the charge into the (almost) dead battery. This is not recommended charging mode, but if the battery is (almost) dead, this mode can bring it back to life.

- slow charge: when the battery voltage has been recovered to more acceptable values (for example, above 9.6 volts), battery charger may start with slow battery charge to prepare the battery for bulk charging.

- bulk charge: battery is recovered, and is able/ready to accept most of the charge. Battery charger charges the battery until the voltage reaches preset value (float or cycle use).

- battery conditioning: when the battery reaches certain voltage and is 'fully' charged, battery is conditioned by applying small current in order to normalize cells.

- battery maintenance: if the battery is left connected to the battery charger, maintenance mode starts - battery charger monitors the battery and charge it periodically with trickle charge, keeping the battery fully charged over longer period of time.

Connecting the fully charged battery to the battery maintainer or to smart battery charger is recommended method for wintering the lead acid batteries, although with newer batteries with 3% or less monthly self-discharge rate there is no need for maintainers at low temperatures for months.

Smart battery chargers also come with many safety features like overcharge/over-voltage protection, reverse connection protection, short circuit protection etc.

But, no matter how safe modern smart battery chargers are, be sure to read their instructions/manuals and to act accordingly. Stay safe!

Long Story Short: If you want to recondition/rejuvenate your car battery and prolong its operating life, get a good, thoroughly tested in real life conditions smart battery charger, take the battery out of your car (if allowed by the car's manufacturer due to many onboard electronic systems powered by the main battery even when the engine is turned off), place it on flat, firm surface in well ventilated area, set the battery charger, connect it and let it do its job.

Again: reconditioning a car battery using baking soda, Epsom salt and similar chemicals - big no, no ... Be smart and stay safe!