Lead Acid Battery Charging, Maintenance Tips

The post discusses some of the crucial parameters related to lead acid battery charging, maintenance tips for ensuring longer life to the device. The questions were asked by Mr. Raja Gilse, answered by me.

What is Full Charge Voltage of a 12V Battery

Q1: What is the full charge volt of the 12 v 110 ah deep cycle lead acid battery at the time of charging? Sir, I am confused. All your article about battery charging you told that, it lies between 13.5 and 14 volt.

I read in some other web sites that, it is 14.4 volt for deep cycle battery  after this point gassing starts. Please confirm me whether this battery high voltage differs with the AHC of battery?

I am asking so deeply because, I have a 12 V 110 ah battery in my house for solar lighting system by the SELCO solar light private ltd, from past 10 years. The charging panel is of 75 watt.

They had maintained 15 V as battery high in their charge regulator. I had noticed that at this level gassing starts in the battery, which slowly spoils battery  So now I made a charger by help of your blog, Now, I am in dilemma to set the bty high volt. So please confirm me the battery high voltage.

A1: It should be normally and ideally between 14V and 14.4V, never above this value. After this level the battery should be applied with a trickle charge voltage or the specified float voltage.

What is Equalization Charge

Q2: What is equalization charge of battery? Is it to give charge up to 15 volt?? Or something else. What is the periodicity of equalization ? Please guide me for my battery's good health.

A2: These are extra maintenance procedures, it's a kind of desulfation of the battery, these procedures will not be required if the battery is charged through a step charger circuit as explained here:


More sophisticated step charger designs can be made by including more number of steps, I'll discuss it soon in one of my upcoming posts.

Charging Current or Charging Voltage What is Crucial

Q3: As you suggested in one of your comments that the 3 step automatic charger is suitable for up to 40Ah battery.

But mine is 110AH battery  So i can't use that. Another thing, further to my earlier email about "battery charging", Which is important thing in battery charging, is it the charging voltage or the charging current? Or both? I am asking so.

Because, in my home, the solar charging panel gives voltage up to 21 volt and 4.5 amps at mid noon. Is it safe for my 12 V 110 ah battery  I read that the max charging volt will not exceed 15 volt . Is it true? Or as the charging current is only 4.5 ah , i.e.

Very much less than C/10, it is safe to charge in 21 volt ?? Therefore I asked which is important voltage or current?

And also in trickle charge , which is important, is it to maintain the charging current as C/100 Or charging voltage as 13.5 ?

A3: It's current that is important, 4.5A will not do any harm to your 110AH battery at 21V as long as it's being charged, however once your battery becomes fully charged then this voltage/current might start causing some concern to your battery, so it's better to keep things regulated and under control. The same goes for trickle charging also, once the battery becomes fully charged maintaining correct voltage (14.4) becomes crucial.

The above section discussed a few lead acid battery charging, maintenance tips, if you have more related questions, please feel free to add them here through the comments below.

Distilled Water Getting Dry

Hi Swagatam

A few days ago, I noticed my 24V UPS batteries get hot (very warm) during charging. The distilled water (electrolyte) is consume quite frequently.

After a close inspection, I found that the some of the cells are not in their normal state. With every passing day, more cells are deteriorating and thus back-up time is also compromised.

The batteries are about 1 year old. Is there some problem with the charging circuit or just the batteries have passed their lives?
Kind regards


Hi Abu-Hafss,
Normally a standard good quality battery will not become bad in one year, and if the water is evaporating quickly that's a clear indication of an over voltage or over current than the specified level to the battery.

You can check the UPS charging current and voltage without the battery connected and compare it with the battery's AH and V rating, that will quickly let you know regarding the situation.

For a lead acid battery Ideally the current should be 1/10th of the AH value, and the voltage a little higher than the rated value of the battery.

Best Regards

Finding Ah of Battery without Load

Hi Swagatam
How do I check the charging current without the batteries connected?

BTW, I do have a DC clamp multimeter; I can check the charging current with batteries connected.

The UPS is compact and light weight.

Kind regards


Hi Abu-Hafss,
If you check the current with the battery connected then you might not get the correct readings, because if the battery is bad then it would resist current and not allow the actual reading to appear.

You can directly connect a DC ammeter at 20 amp range across the charging leads without any battery, just for a couple seconds only, and that would allow you to get an idea regarding the maximum capacity of the charger.

If the charger is equipped with a current control facility (which it should) then the reading will be as per the battery specs, or if the charger is incorrectly built then you might see an abnormally high reading.

Best Regards


6 thoughts on “Lead Acid Battery Charging, Maintenance Tips

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. what if you're using transformer of 12vac,which has a peak of 16 or 17vdc after rectifier & capacitor.is this voltage ok? with 10% of the battery amps i.e charging the battery of 70amps @ 7amps with that peak voltage

    • you will need to check the current and the voltage with a DMM after connecting the batt to the supply, if the readings show within the specified limits then it would be fine.

  3. the current is ok. but the voltage reads peaks of 12vac. which is 17vdc using DMM .is this voltage ok since it the peak voltage of 12vac

    • Did you connect a discharged battery with the supply?

      The voltage and current must be checked after connecting a discharged battery, if still it shows 17V then it can be dangerous.

  4. when the battery is partially discharge all the way to 12.4vdc,the charger reads 13vdc using DMM.but wen the battery is fully charged it reads between 16vdc with current of 0.5amps.so is the charger safe to use?

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