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How to Calculate the Battery Charging Time & Battery Charging Current – Example

How to Calculate the Charging Time and Charging Current for Battery Charging?

Easy Battery Charging Time and Battery Charging Current Formula for Batteries. (With Example of 120Ah Battery).

Battery Charging Current and Battery Charging Time formula with 120Ah battery solved examples

In the following simple tutorial, we will show how to determine the suitable battery charging current as well as How to calculate the required time of battery charging in hours with a solved example of 12V, 120 Ah lead acid battery.

Below are the given formulas for required battery charging time in hours and needed charging current in amperes as follows.

Charging Time of Battery = Battery Ah ÷ Charging Current

T = Ah ÷ A


Required Charging Current for battery = Battery Ah x 10%

A = Ah x 10%



Calculate the suitable charging current in Amps and the needed charging time in hrs for a 12V, 120Ah battery.


Battery Charging Current:

First of all, we will calculate charging current for 120 Ah battery. As we know that charging current should be 10% of the Ah rating of battery.


Charging current for 120Ah Battery = 120 Ah x (10 ÷ 100) = 12 Amperes.

But due to some losses, we may take 12-14 Amperes for batteries charging purpose instead of 12 Amps.

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Battery Charging Time:

Suppose we took 13 Amp for charging purpose,


Charging time for 120Ah battery = 120 ÷ 13 = 9.23 Hrs.

But this was an ideal case…

Practically, it has been noted that 40% of losses occurs in case of battery charging.

Then 120 x (40 ÷ 100) = 48   ……   (120Ah x 40% of losses)

Therefore,  120 + 48 = 168 Ah ( 120 Ah + Losses)

Now Charging Time of battery = Ah ÷ Charging Current

Putting the values;

168 ÷ 13 = 12.92 or 13 hrs. ( in real case)

Therefore, a 120Ah battery would take 13 Hours to fully charge in case of the required 13A charging current.

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  1. there is some error in calculation for 120 ah and 13 amps it would be 9.23 bt u have type as 150 instead of 120 so change it

      1. sir i want to install a 1 kw solar pannel in my home . so i want to know how many battery i will connect. i want to connect 2 battery of 150 ah , can i ?.
        and also tell me charging time and backup time of batteries ,thanks sir

        1. If you want to connect 1kilowatt solar panel first of all you have to buy a 1700va/24V PCU(power conditioning unit////0 of Smarten company then you can connect your 1kw solar panel on that product and also you can use your 2 batteries of 150ah.
          1kw solar panel will produce a peak current of near about 32Amp. which will charge your battery in near about 5 hours.
          Go for Smarten Solar PCU they are the leading manufacturers of solar PCU.
          Solar PCU is a device through which you can directly connect your solar panel and your battery charging will start without any solar charge controller because it has a inbuild charge controller.
          And if you want to continue with your existing inverter then you can buy Smarten 24V/50Amp. Solar charge controller. After installing this device there is no need to replace your existing inverter.
          If there will be any query you can ask me anytime at….Thanks!!!!

    1. It will not be 9.23, depanding on battery internal resistance it will go to CV mode charging. Chargin will take from 9.5 h up to 12h depanding also on end of charge current.

      1. But iam using 40Amps for 48v150AH battery charging

        But battery is TAll tubular so I think perfectly okay because still now running 2 and half years (this is solar inverter using advanced inverter)

  2. Most battery manufacturers recommend sizing the charger at about 25% of the battery capacity (ah = amp hour capacity). Thus, a 100 ah battery would take about a 25 amp charger (or less). Larger chargers may be used to decrease charge time, but may decrease battery life. Smaller chargers are fine for long term floating, e.g. a 1 or 2 amp "smart charger" can be used for battery

    1. This depends on the type of battery. Traditional flooded batteries safely accept about 12% its AH range, GEL about 25%, and AGM 33%.

    2. HELLO I AM LOOKING FOR A li polymer battery 3.7v 120 mAh/15c for a rc helicopter but i find a
      3.7 v 175 mAh or another with 200 mAh and i dont know if it will work or whats the difference i hope you can help me

      1. You can go with 3.7 v 175 mAh or 200 mAh instead of 3.7v 120 mAh/15c. The only difference is that both the last mentioned batteries are stronger means it will work for more time.

    3. sir weve been assembling our battery charger and sold for very long time but until now i could not determine the exact output amperes of my charger.weve just limit the output charging amperes at 6 can charge upto 15 different size of batteries. weve just determining the battery charged by using battery load tester and hydrometer tester.what tools were used to determine the output ampere of the charger.many of our assembled chargers still on working condition for more than 10 years.sales so slow for us.

  3. i have battery in my home with ups<br />NS-175 of Osaka company <br />how i find its voltage nd ampere-hour rating…???<br />plz tell me<br />

    1. no dear its wrong perceptions in these days model of battery doesn&#39;t mean that battery contain same ah thats why battery life go down because majority dont no this fact . NS-175 dont contain 175 ah as well its hardly 130 or 110 which differ in brands of batteries as well .real example i have ags 190 batterie is (ah is 150),phonex 205 battery ah is 145 .these ah details are provide by official

      1. Its is True. There N-175 means model not AH. I have gone thorough many shops for local brand but they did not tell me the actual AH or Crank Power . thats is why you will not get the good back time even u have the best ups (APC ) and properly care the battery.

        1. Pls help.
          My ups is of series. Of two battery rated 12v 7.5ah each .
          Now wanna convert to inverter. What charger capacity should I use if I were to use a 12v 45-75ah. Or if I were to combine 2 battery of 12v75ah.
          Can I use a single battery yet give the output expected of series .
          If I were to use a single battery
          If I were to use 2 battery
          I need advice

    1. Just check the battery Code like NS-200, NS-175, NS- 120. <br />So these are it Ah rating for instant, NS-200 = 200Ah, 12V.,,and we also know that these battery comes in 12V DC.

  4. could u please tell me how to increase the battery power..what are the specifications to be considered while bying a new ups…?

  5. If i have a battery bank as follows:<br /><br />25 batteries(12v) x 120 Ah = 3000 A<br /><br />So in this case I need 300A rating for charging?<br />In this case I need charge controller for 300A?<br /><br />Please can you help if this is correct?

    1. Dear,,,, 12V batteries comes in DC, while 220V is AC….. and we cant not store AC in batteries. <br />Also the question is irrelevant, but refer to basic calculation<br />12V x 120Ah = 1440Wh<br />and for 220V <br />220V x 120Ah = 26400Wh

      1. Dear sir.
        My AGS battery getting low gravity. Plz tell how to fully charge it with ups. My ups not charging it full. Output timing is very short. The battery is new. 6 months old.

  6. Hi friends, I bought electrical scooter (Its name is Volta VS4 3000W, made in Turkey) . It has 60V,20A gel accumulator and charging valuse are 60v and 3A. How long does it take caharging time? User guide explains charging time is nearly between 6-8 hours. How can I find these charging durations?<br />Thanks

    1. The accumulator [Battery] rating should be 60V, 20Ah.<br />Thus charging current for 20Ah would be 10%. of it rating [20Ah].<br />Therefore, [20Ah x 10]/100 = 2A.<br />Ideally, the charging current for this battery would be 2A.<br />but due to losses, we can take 2-3A for charging propose.<br />Now charging Time = Battery rating / charging current<br />= 20Ah / 3A = 6.6Hrs. ideal case.<br />Due

  7. Hi sir ur blog is superb..<br /> i hav a general question that what will be the discharging time, and load capacity of a battery, how we can calculate that..

  8. Hi, my solar energy system comprises a 200watt-solar panel, a 10A(12/24volt-charge controller), 2 120Ah batteries and a 1000watt-invertor(24volts). How should I efficiently charge my batteries: in series or in parallel. Also, is it possible to watch TV while charging in parallel?

    1. It not possible
      What is the current of the panel?
      If you are using 200w for 1000w inverter you need at least A (35v 9a 200w panel)*2 in series +B (35v 9a 200w panel)*2 in series . then add A and B in parallel connect to charge control can be 100A effective solar connection
      To manage you can use 200w 8A 24v panel in parallel * 4panel charger controller 30A if have more suning weather condition
      U can call +2348060643549 +2349076066319

    1. Yes – But starting current the Solar control Panel will take from other available source. Please remember 1000 W means 700 to 800 W power that you can take from Solar panel. Also AC should be having Inverter technology.

  9. sir my dry cell battery of indus company is(33ah/20h) so what will be the charging current n time of the battery?(plz tell me wid formulae)

  10. Dear Sir,<br />i understood your explanation but was confused a little. Is the fixed rate 10% for charging current and can be same the rate charging with Charger, Inverter and Solar? let me known clearly, Sir?

  11. sir, <br /> 130ah /12 vdc 8nos batteries in series so what is the correct charging current for this tubular batteries …i am some what confusion pls clear

  12. hi,<br />Do you know , what is the relation between charging time, voltage , capacity, charging current in lithium ion rechargeable battery.<br /> suppose how much time it will take 6000mah battery charging with 100mA with 4.2 volts.

  13. Sir,<br /><br />I have read your explanations thoroughly and you have done a brilliant job.<br /> <br />Sir I have a query &quot;Can I charge 12V, 150AH +150AH Tubular Batteries in parallel with 135 Watts Solar panel along with 875VA Square wave Inverter&quot;.<br /><br />and one more query &quot;Can I directly connect Solar Panel to Batteries w/o using Solar Charge Controller&quot;.<br /><br />

  14. Dear Sir,<br />It is really nice to visit this site for conceptual clearing and its application. May i know that 4 number batteries of 12 v, 200 Ah connected in series would consume/require how much units of electricity when being charged with 220 v, 50 hz AC supply in 6 hours.

  15. sir..i have microteck sine wave inverto SEBz 850VA, and i bought the Luminius Tubular battery ILTT18048 150AH. The proble is the invertor is unable to charge the battery.<br />The battery person came twice and checked the battery and told that the battery is fine and told me to check the invertor.<br />I took the invertor to local checking center and they told is invertor is fine and giving 8amps

  16. Sir, I have two local made with 500 VA rating while the other is Mikrotek 1100 VA, power supply is very less in our place..sometimes about 5 hours a day…so to reduce the charging time can we connect both the inverter to the same exide tubular there any bad effect of doing so..?? plzz suggest.

  17. you have not factored in the charge voltage. 14.6v is much faster than say 13.6v. nor have you considered a 120Ah battery should only be discharged to 60Ah (50% of its capacity). also, you are assuming the top 20% of battery capacity (80-100%) is replaced at the same rate as the first 30% (50%-80%). this alone throws your charge times way, way off.

    so, 50% of available capacity = 60Ah… at 14.6v and 13a, it would take about 3 hours to get from 50% – 80% available capacity. but then, as the battery builds up resistance, the amps begin to taper off, and taper off more quickly as the battery becomes increasingly charged. so by the time it’s at say 90% charged, it may only accept about 5 or 6 amps. so, the charge rate decreases and charge time increases significantly, as the battery becomes more charged.

    if the battery had a capacity of 240Ah, and was discharged to 120Ah, (like your example) it would take about 6 hours to replace 72Ah (50-80%), and significantly longer to replace the other 48Ah (80-100%); keeping in mind 14.6v would not really get you to 100%… this would require a higher (equalizing) voltage of say 15.5v for several hours. so your formula is way off! replacing 120Ah with a 13a charger would require at least 24 hours.

  18. Hi,

    I got a battery with specifications on it

    Nickel Metal Hydride Rechargeable Battery

    Output: 10.8 Volts 2100 Ampere Hours

    but i want to make a circuit for charging the above battery

    so for the purpose can you tell what are the Voltage and Current needed to charge the battery

    the method of calculating it

    and what is the result if i give more charging (in Voltage and Current) than it required

  19. when solar is connected to the batery and batery is connected with invertar and inverter is connected with load , then question is that wheather load takes power from batery or solar pannal?

    1. In this case, Solar panel performs two jobs viz Storing energy in the Battery and Supplying power to the directly connected load. For More Detail… Check this link

  20. How long will it take to charge 32 batteries of 12v by 200ah with 23 amp inverter? (Have charged the batteries for 50hrs and and they are still indicating low battery charge)

  21. How long will it take to charge 32 batteries of 12v by 200ah with 48v 23 amp inverter (the batteries are connected four in parallel) so far I have charged the batteries for 50 hrs but their charge indicator is still low

    1. I am no expert but I will take a shot at this, though your question was a year ago and I assume you got an answer by now! You have 32 12 v batteries. You say they are in PARALLEL in groups of 4, but you probably meant in SERIES in groups of 4 as you indicate that you have a 48 v system. So in effect, you have created a 48 v 200 ah battery out of each group of 4, and you then tied 8 of those groups together in PARALLEL to form a system of 48 v 1600 ah. You advise your charger provides 23 A @ 48 v, so if your batteries were completely discharged (which they never should be, and not accounting for the losses due to inefficiency of the charging process which others on this site indicate are as much as 40%!) it should theoretically take about 70 hours to recharge your system. In real terms, much longer. However your system probably is never discharged more than about 50% but factoring in that inefficiency, your net real world charging time is still right around that 70 hour mark in my estimation. I welcome comments from others if my above reasoning or calculations are incorrect!

  22. I have a tab. the battery info 3.7v and 13.0 wh , li-lon battery capacity 3500mAh. i can not understand how charger use volt And ampear use it .
    please tell me charger out put rating . i use?

  23. My Panasonic’s 100Ah 12V VRLA battery charging method says “initial current 15A”, so it is 15% right?

    My question is, when I connected two of the batteries in series, does that make the charging method initial current 30A?

      1. Sorry, I meant to say that I connected the two batteries in parallel, the initial charging current would double right?
        Also, why is it called “initial” ? Does this indicate that if I am charging the batteries using a Solar Charge Controller, where the initial charging current of 20A increases gradually as the sun noons until the charging current exceeds 30A and reaches say 35A, would it damage the battery? Whats the tolerance of exceeding “initial” charging current..

  24. Sir, I have two local made with 600 VA rating while the other is Luminous 650 VA, power supply is very less in our place..sometimes about 6 hours a day…so to reduce the charging time can we connect both the inverter to the same ADDO tubular battery there any bad effect of doing so..?? plzz suggest. and how connect them

  25. Dear sir, I have 5 batteries of 12 volt 65Ah each connected in series to get 60 volt. Please tell me the suitable charger to charge these batteries in 8 or 10 hrs. Please mention charger voltage and current.

  26. I have 12v- 135AH battery, now the br is going to weak with 5th cell, can i connect the br or any condition br. with computer ups for using load one tube lamp and fan purpose. usually computer ups output load is 600w, can i 300 to 400 watts load with heavy ah br like 100,120,135,150, Is it make damge the comp. ups or not kindly reply me.

  27. can i connect two computer ups with the above br 135/150ah I know the charging time will take more , while the charging op volt 12 with below 1amp for charging the ups br for 9a/20h

  28. I have been having some trouble figuring out what the charging current for a set of 4 (2.9Ah 12V DC) lead acid batteries would be when hooked up in a Series-Parallel circuit. (Here is a link to the diagram: It’s figure 12.) Well I am using it for an old electric scooter and it has a 24 volt motor, but the original two batteries intended to be hooked in series could not be found. So my question is What current should I charge it at? (I am using an RC battery programable charger that has lead acid chemistry as one of the presets.)

  29. If a battery bank of capacity 2000 Ah ,48 V drives a load of 1.5KW for 2 Hrs,what capacity and voltage of the battery bank will be after 2 Hrs? And after 2hrs if the battery bank start charging with a voltage of 55V,then how much time will be required to charge the bank fully?…………Please help me ,with detail answers and tell me the formula for calculating the voltage drop of the bank after 2 Hrs discharge

  30. dear sir thanks for great information
    I have a question if you can help me

    I have tow 12v 150AH batteries connected in parallel to 3000watt inverter and 20Amp charger
    300 Ah batteries should charged with 30A charger ( 10% ) witch i don’t have
    will it work ( charging ) with 20A charger

    please i need answer .. sorry for my poor English

  31. I have Phoenix USG175 Battery, which is around 2 years old but going awesome:) 4+ hours of backup (1Fan, 1TV, 1 Energy Saver 1Laptop) but its plates changing its color to black, I checked its charging ampare set at 18, i have changed it 13 amp and cut off volt at 14.40 v . Is it correct combination?

  32. pls….help me….can a 2v , 300Ah battery be replaced
    with a 2V, 200 Ah battery for a 24V, 300 Ah capacity battery bank?

  33. pl let me know how many battery i need and charge controller specs for 200×5=1000w solar pnnel each 200w@24V to get max power utilisation.

  34. I have an inverter with specs 1000VA, 900Watt, 12V DC, 230V AC.
    How long it will take to charge a battery of 220 Ah with above specification
    Please suggest thanks

  35. I have simply made A battery charger with microwave transformer,But when I connect to battery high current flow and diod Bridge rectifer burnt, Although I have used 40 Amp bridge rectifer and battery taking 20 amp
    if any body know solution plz tell me

  36. Hi, Im planning to buy a PIP-4048HS inverter charger from MPP Solar and charging via utility is 60amps. How long will charge a 48v 200ah system. secondly, if full charged, how long can the battery power a 2kw load?

    Thank you.

  37. If you were to charge 12 V ,120 Ah lead acid battery in Europe & USA where supply Volage is 240 V & 110 V……will the time taken to fully charge differ ?

  38. We connected a 1KV / 24Volt solar inverter system.

    Load = 150Watt flood light

    Battery = 2 Batteries of 12Volt 65Ah in series to make = 24Volt 65Ah Battery bank

    Solar panels = Qty 4 of 250Watt ; panel specification : 33 Volt, 7Amp each

    Now current meter is showing charging current = 1.3 Ampere Only

    Why it is not increasing ?, I think it should be more about 5 to 6 Ampere to charge 65Ah Battery.

    Please clarify this.

  39. Sir I have an ups system installed in my home. The inverter is of 720 watts and my battery is 200 ah. Now I have two panels of each size is 58 inches long and 27 inches wide. Plz tel me that how many watts and volts are generate by each panel . and how could I connect these panels in my inverter. In series or parallel. Also tel me how to calculate the watts and volts of the panel. Sir my inverter has also solar supported.

  40. Spinoff question:
    Lets just say i only have access to 7ah batteries… if i were to put 20 of them in a parallel do i still need to charge at the 7ah rate (.7a) or is it safe to charge at the 140ah rate (14a)? Or somewhere in between?

  41. Dear Sir,
    I have purchased 135Ah AGS battery. How many watts i require to charge it if sunshine is 6 hours. It need how much current(A) to be optimally charged.

  42. hi.hi i have 125ah battery . i made a charger of 12.7v 12amp. but charger heat up too much. espcialy diodes . i used 6amp 12 diodes in bridge rectifier. but still so heatup ang battery not charg fully. plz guide what should i do.

  43. I have 200A excise battery with microtech 1125 inverter. but supply is about 10,14 hrs in a day. I have 2 solar pqnnel of 75 watt each. sud I connect those pannel for charging the battery? panel will give 3 to 4 A each….sud I connect them in parallel?

  44. Dear sir kya 12v 200ah ki battery ko 12v 5 amp ke charger se full charge kiya ja sakta hai. 200ah/5=20 hours ki nahi. Ya mujhe 20 amp ka charger use karna hoga. Sir charging current battery rating ka 10% kyo hai kisi website me nahi hai. Plese reply jarur de.

    1. Dear Reetesh,
      battery ka rating ka 10% isliye lete hai ki mera battery achche se charge ho. ise humlog C10 bhi kahte hai. this is standard charging and good for battery life. aisa nhi hai ki kam current se charge nhi kr skate, jitna kam current se charge karege utna hi battery charge thik hoga but time jayada lagega.
      Ex. 120Ah battery
      120/20 = 6 amp charging current rate for 20 hrs.

  45. Sir
    mera 200ah ki battery hai aur 150 w ka solar cell to kuch v charge hota hoga ya bilkul nahi
    Yadi 200 ah ki batry ke liye 300 w ko solar cell laga dege to batry kharab ho jayegi

  46. I have a 48v inverter and I wan to get 24 2v batteries to power it for lighting. what capacity of charger can I use as back up charger?

  47. Dear sir,

    how can i limit the charging current of 12 volt solar plate to charge a 12 volt, 4 amp lead acid battery.

  48. Hello,

    I have 108 VRLA cell of 2 Volt each. Finally its 220v/300Ah, so my question are

    1 – Charging voltage in float mode?
    2 – Charging current in float mode?
    3 – Charging voltage in Boost mode?
    4 – Charging current in boost mode?

    Please answer.

  49. I have 100*7AH batteries
    I require to charge these batteries by another battery bank and
    Now how much capacity of battery should i require to charge those small batteries considering 50% DOD of battery and 80 % efficiency, and how much power should i require to charge battery bank with solar (consider 6 Hours of Peak)

  50. I got a DC generator with 75V and 12KW, is used for charging the battery bank to 64V and 450AH, KDZ 2701 model.
    I would like to know which current is consumed by the Bank of the batteries and the charging time, after a discharge (1200A) of 1 minute.

    1. What is the wattage = IV divided the wattage
      Energy input = energy output
      12000w * t = 64 *450AH
      Current consumed by battery power bank is 450÷10=45a

  51. i am also trying to understand and going to installation of solar panels
    as i am already electrical technician

  52. Hello

    Can you explain , we have 450Ah battery 110V , but 430Ah Battery charger . what will happen if we can use this battery charger (430ah)with battery(450ah).

  53. Sir i have make a loop 32 Batteries in such a way that 4 batteries are series (mean 8 series sting) and than these 8 series sting are than parallel with each connecting to two 5kw inverter which are parralel with each other.. So what will be my batteries charging time.. How i calculate my batteries charging time??

  54. Hi How long would 2 (new fully charged to 13v) 12v 130ah deep cycle batteries making 24v power a 24v outboard motor at full speed 55a and half speed 30a before they dropped from 26v to 23v? Thanks

  55. Is this formula for charging current applicable to batteries with different C Rating?
    From the look of it, it seems like applicable to only C10(C/10) batteries?
    Please correct me if I am wrong. I am trying to find the maximum current requirement to charge a C20 battery.

  56. 2 selling fan 5 watt ka 10 led. 10 ghanta ka bachup chahiye Kitna Ah ka baitry or Kitna wathh ka mono solar or Kitna VA ka soler inverter lagega

  57. Please, I am confused on your explanation on the relationship between charging current formula as you give to be 10% of battery Ah, and you used that to determined the charging time and the number of solar panels required for a particular case. But, I observed that on the solar panel specification label, you may find current at the maximum power to be lower than the calculated one. Now, the confusion is that the label figure do not tally with the one calculated from your explanation if I really grasped it. Please, bail me out. I want go for DIY procedure to curb cost.

  58. Sir,,,,i use 200ah tall tubular battery of amaron company… battery rating is 200ah….can i supply charging current 14ah to charge the battery????can 14ah charging current is higher to charge the battery????can it decrease battery life span????

  59. Charging current for 120Ah Battery = 120 Ah x (10/100) = 12 Amperes
    Can you please elaborate this because I’m confused. The unit of Charging current is Ah (Amp-hr) then you multiply it to 10%. How come the unit became Ampere? why you remove hours? please…

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