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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

Below is a simple battery charging current and battery charging time formulas with a solved example of 120Ah lead acid battery

Here is the formula of charging time of a lead acid battery.

Charging time of battery = Battery Ah / Charging Current

T = Ah / A


T = Time hrs.

Ah = Ampere Hour rating of battery

A = Current in Amperes


Suppose for 120 Ah battery,

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 Amp.

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, an 120Ah battery would take 13 Hrs 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

    • Electrical Technology

      Dear Sudharsan M,U@<br />Thank you so much for taking a valuable review.

      • 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

  2. Electrical Technology

    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 &quot;smart charger&quot; can be used for battery

    • Tyson @ Fullriver Battery

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

    • 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

      • Electrical Technology

        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.

    • 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 amperes.it 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 />

    • Electrical Technology

      The rating of Osaka NS-175 battery is ( 12V, 175Ah)

    • 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

      • 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.

  4. thanks <br />but can u telll how u find it??so that next time i also find it<br />plz

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

  6. 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?

  7. sir i want to ask you that There is no difference in the 12v 120Ah and 220v 120Ah<br />

    • Electrical Technology

      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

      • 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.

  8. 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

    • Electrical Technology

      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

  9. Sudheer Reddy Marala

    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..

  10. 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?

  11. hi sir… what can i do to improve the efficiency of the cahrging time? means to make the charging time is less<br />

  12. dear ser weare charging 300 ah batery 10 hr with 10 amp then howmony unit corrent is taking from electricity

  13. Electrical Technology

    Wrong Q dear..

  14. dear sir how can I find out that what ampere current my 12 volt<br /> charger produce


  16. Sir can I run 1 Ton AC on 1000watt solar panel.

  17. sir , my battery is (33ah/20h) so what will be the charging current n time of that battery? <br /><br />

  18. 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)

  19. 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?

  20. 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

  21. naga raju maalothu

    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.

  22. Dear Brains,. Pl…guide me how to CHARGE 12 Volt/220 Ah, 12 Batteries Connected in SERIES.

  23. 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 />

  24. 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.

  25. 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

  26. Sir, I have two inverters..one 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 battery..is there any bad effect of doing so..?? plzz suggest.

  27. Please tell me the charging time of a mobile battery like as 800mah 3.7v

  28. How should i calculate the charging time of 2V, 2000Ah battery. should i follow the same as 25% current loss.

  29. 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.

  30. 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

  31. 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?

  32. pls….how Long would it take two 115ah batteries to be fully charged by an inverter (1.5KVA).12V battery.

  33. 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)

  34. 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

    • 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!

  35. how much current required for 220ah battery

  36. tell me how much current required for 220 ah battery. ..Please tell me any one of you

  37. 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?

  38. 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?

    • Electrical Technology

      Yes! It is….

      • Narendra raI

        ElectrIcal Technology

        student . b.tek

      • 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..

  39. Sir, I have two inverters..one 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 220Ah..is there any bad effect of doing so..?? plzz suggest. and how connect them

  40. 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.

  41. 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.

  42. 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

  43. how much power will be consumed to fully charge a 12v 150AH battery. please give me the calculations..

  44. 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: http://www.batterytender.com/Connecting-Chargers/ 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.)

  45. Sir,

    Can you please tell me how to calculate the current of a 5kW/240VDC Battery charger?


  46. 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

  47. thankyou sir , its really helpful

  48. 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

  49. 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?

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

  51. 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.

  52. 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

  53. Which charger can I use for 100ah and 135ah Or more than 100ah battery pleas reply to this message thanks

  54. 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

  55. i have a 175 ah battery how can i charge it..

  56. 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.

  57. 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 ?

  58. 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.

  59. 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.

  60. 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?

  61. 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.

  62. Sir, may you tell me the formula for calculating charging current required for formation of plates

  63. 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.

  64. 200ah battery kitne unite bnaygi full chage hone k liye

  65. 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?

  66. 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.

  67. Sir 200ah/5 amp= 40 hours hai please mere phale ke comment ko thik kar lena

  68. 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

  69. 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?

  70. Hello,

    You can calculate current, capacity and voltage of batteries connected in series or parallel with a simple calculator available online here : http://www.power-calculation.com/battery-storage-calculator.php

    It gives data for individual battery and for the whole system of storage.


  71. Dear sir,

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

  72. 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.

  73. 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)

  74. How to determine the discharging current in a battery?

  75. 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.

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