How to Remove Lead Sulfate Buildup

The battery i hade was a motorcycle battery ytx12-bs. This battery had 10 Ah capacity brandnew but after 3 years the battery wasn’t able to star the bike and the capacity was 900mah. I open the battery and i put distiled water in but the battery voltage was low, about 11.9 to 12.1 volts after charging it with a conventional battery charger and the capacity increased to 2 Ah. After 2-3 bays it couldn’t start the bike. A smart battery chargers can ditect the state of the battery and charge it properly. The problem is that the max volatge that they will charge the battery is 14.4 volts and some 13.4 volts. That will remove some sulfate and the battery capacity will go up. The problem is when the charger would not axept to charge the battery. To solve this you can use and old battery charget that isn’t smart, conect the battery to the charger and let it charge for 24h. So to do a better good i conected it to constat current , constat voltage power supply. I charged the battery up to 14,7 volt with a current limit of 2 amps. The battery stared making bubbles because of the electrolises that was taking place and the temperature went up a little. After fully charging and discharging the battery 2-3 times the capacity went up to 4Ah and then i increased the voltage to 15.5 volt. When the battery volage went to 15.5V i left it another 8 hour the first time and for 12 hours the second time, so that the electrolises had time to clean the plates and break down the sulfate. The capacity went to 9Ah. It is holding great after a month and the capacity has gone to 8 Ah which is ok. I chargsed the battery at 14.4 volts with 1.5 Amps to do the capacisty tests. All the discharge testing was done down to 10.5 volts with a 10 Ohm load. After the discharge tests the volage with no load of the battery was 11.4 -11.5 volts. After charging to 14.4 volts the battery voltage droped to 12.5V. I think that i probably have a problem with the electrolyte and i will put some epson salt to fix this and increase the voltage and the cracking amps.


Step 1: Add Distiled Water

Add distilte water. You can also measure the SG of the electrolyte after adding the water. If it is low you can and some epson salt or buy new electrolyte. The SG depends on the state of charge and the battery type, so you have to find the right value for your case. The averege SG for lead acid battery used in vehicles is

100% charge  1.265

75%    charge 1.225

50%    charge 1.190

25%    charge 1.155

Discharged    1.120


Step 2: Charge


Charge the battery with high voltages up to 15V and let the battery to by electrolysed for 5+ hours. Then discharge to 10.5 volts. The battery current when charging and discharging must be C/10 or C/5 and lower for better results, especially at the first charging and discharging cycles but you can go higher if you want. The C Rate refers to the rate at which a battery is charged or discharged. If we have a 10Ah battery then 1C is 10 Amps, 0.1C is 1Amp and 2C is 20 Amps.

Step 3: Repeat

Repeat the Step 2. 3-4 time. You can measure the capacity of the battery when discharged it. A good idea is to buy a battery capacity tester, it is very easy to find something on ebay under 5$. The voltage of lead acid battery when stored should not go under 12.6 volts. You can charge the battery and then lower the charging voltage to 12.6 volts in order to maintain the battery at a full charge, if you are not going to use it for some time. Also you can test to let the battery unconneted and see after 2-3 days how much the voltage and the capacity dropped. It is normal to decrease but not by a lot.

Some Useful Info








  • Battery voltages vs capacity see the photo. This photo show the battery voltages after
    charging the battery and letting it unconected for some time.

  • Battery capacity and voltage will drop if you let it unconected for a long time.

  • Epson salt don’t increses capacity only the cracking amps and the voltage to the battery

  • If your battery voltage is to low less than 9 volts or doen’t hold a charge then you will have to to dump the old electrolyte, clean it with soda water and put another electrolyte like epson salt.

  • If you don’t have enough cracking amp you can put a capacitor in paralel with the battery 16-35V with 1-2 Farad capacity. Epson salt will help with the cracking amps to.

  • Desulfators don’t work. You will have better results just by fully charging the battery.

  • The cut off charging volage sould be 13.4 to 14.7 volts. After charching the battery voltage dropps to 12.7 volts.

  • Discharge cut off voltages depends on the discharge amps.

  • To increase the life of the battery you have to fully charge it up to 14.4 volts every 3-6 months
    and add distiled water.


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