DIY Recover Sealed Lead Acid Batteries

diy_39featAs I mentioned in a previous article, knowing how to recondition or recover used batteries is a valuable skill from both environmental and economical perspectives. Some of the most popular and widely used batteries nowadays are lead-acid cells. They are the oldest type of rechargeable batteries, the first version being invented in 1859 by Gaston Planté. In spite of offering low energy in comparison to its weight or volume, they can deliver relatively high surge currents. This and their relatively low cost have made them very popular in motor vehicles, whose starter motors require such high currents.

Large scale lead-acid designs with improved storage times and reduced maintenance requirements are also used in cell phone towers, hospitals and stand-alone power systems. They are collectively known as valve-regulated lead-acid or VRLA batteries and they are based on gel-cells and absorbed glass-mat. Since VRLA batteries do not require regular checking, they have been called maintenance free batteries. However, the electrolyte inside may escape if it cannot keep up with the chemical reaction and the cell will lose capacity. Should you ever use VRLA batteries or if you’ve already got some, make sure you regularly measure internal resistance, conductance and impedance.

As we discussed in a previous article, batteries lose their properties due to sulfation or the crystallization of lead sulfate on the plates. When it’s new, the lead sulfate reverts to lead, lead dioxide and sulfuric acid very easily and completely. As the battery goes through numerous cycles of charging and discharging, some of the lead sulfate is not recombined into the electrolyte and slowly crystallizes. Sulfate deposits expand and ultimately crack the lead plates, destroying the battery. You can tell if it’s happening to you if you start noticing longer charging times, less efficient and incomplete charging, and higher battery temperatures.

A battery is unrecoverable if the active material is lost or if the plates are bent or cracked. This may come as a result of overcharging or high temperature. While high temperature leads to sulfation, overcharging leads to corrosion. Unless the plates have cracked, you can use pulse conditioning to reverse the sulfation process. High current pulses produced between the battery’s terminals can break down sulfate crystals. The pulse must last longer than the resonant frequency of the battery. Since it takes very long, electronic circuits can be used to regulate pulses of different widths and frequencies. There are many battery pulse chargers available in commerce. Here is an example.diy_39.3

If the plates are all right, you can restore a battery by simply “rehydrating” it. If the battery was not left alone for more than 5 years, you can restore it to 99%. If it was unused for longer, it will recover up to 50-75%. The plates in the picture were recovered from a 6V lead acid battery. We will only recover batteries that have dried off. The broken plates need replacing.

Step 1: Materials required

  • A sealed lead acid battery

  • A syringe

  • 50% sulfuric acid (H2SO4)

  • Pure water

  • A Beaker

  • DC power supply

  • A sharp pointed tool

  • A multimeter

Make sure you get rain water or battery water. Don’t use tap water. The beaker can be made from plastic or glass. The DC power supply must match your battery. If you haven’t got a multimeter, you could just use a LED. You could also use a Y tube and wires or clips, but they’re not a must. Make sure to use safety gloves and goggles. The acid in the battery might leak. It’s so corrosive, that it can eat through your skin in a matter of seconds.


An initial reading of the plates showed 0V.

Step 2: Open the cap


The two batteries in the picture have 4V and 6V. Using the pointed tool, open the plastic cap and remove the round rubber lids.

Step 3: Rehydrating

diy_39.7Fill the syringe with water. Use it to pump water into the battery until every cell is full. Leave them for a while, then close the lids and cap. Be careful not to overfill. You should use acid if the battery hasn’t been used for more than 5 years. Make sure to dry the battery of water before you do that.


Step 4: Charge the battery

diy_39.9Connect the battery to a matching charger. Be careful not to overcharge. It’s safe to use 1V more than the battery voltage. Don’t worry if it gets a little hot. Leave it for a while and test the power every now and then. You can use a multimeter or a LED to check it.diy_39.10

As you can see in the picture, the battery has charged nicely. If it didn’t work with water, try repeating the process with acid. If it still doesn’t work, it means that the lead plates are dead.

Every day we rely heavily on all sorts of batteries. If you think about it, there’s at least a battery in each of our phones, cars, watches, alarms and in many other devices. With ever increasing levels of environmental waste and pollution, any knowledge allowing us to reuse resources is welcome. Even more so if we are talking about batteries or other things that can be very harmful for the environment upon their disposal. You could also leverage this skill in a TEOTWAWKI scenario. With commerce dead, your survival will depend on the skills you bring to the table. Being able to restore batteries could be a very valuable skill in such circumstances.





How much do you spend on SLA batteries per year? Share your thoughts in the comment section below.


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