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

How to Calculate the time for battery Charging?
Easy Charging Time Formula for Batteries. ( with Example of 120Ah Battery).
Charging Time and Charging Current Formula for Batteries with Example of 120Ah Battery

 Here is the formula of Charging Time of a Lead acid battery.
Charging Time of battery = Battery Ah / Charging Current
 T = Ah / A

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.
so charging current for120Ah Battery = 120 x (10/100) = 12 Amperes.
but due to losses, we can take 12-14Amperes for charging purpose.
suppose we took 13 Amp for charging purpose,
then charging time for 120Ah battery = 120 / 13 = 9.23 Hrs.
but this was an ideal case…
practically, this is noted that  40% of losses ( 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
168 / 13 = 12.92 or 13 Hrs ( in real case)

 Therefore, an 120Ah battery would take 13 Hrs for completely charging ( with 13A charging current).

By: Wasim Khan

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Electrical Engineer. Writing for www.electricaltechnology,org You can contact us via Email or on Facebook. follow us on Also, Follow


  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

  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

  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 />

    • 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

  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 />

    • 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

  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

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


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

  16. 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?

  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. 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

  20. Sir,<br />I want to buy an inverter &amp; battery. My wattage usage are approx 300 – 350 . I want to run inverter around 10 hour/day. Plz suggest : 1) inverter VA &amp; respective battery AH for above requirement.

  21. Sir,<br />I wanr to buy an inverter &amp; battery. My wattage load is around 300 to 350 watt. Plz suggest Inverter VA &amp; corresponding barrery AH to fulfil above requirement.

  22. Hi .. Good day <br /><br />I have a question <br /><br />I have two banks of batteries and two battery chargers in parallel 48cvd <br /><br />and a total current of 35 amp, i thought that was going to of dividing the current in half <br /><br />but charger was left with 10 and one with 25 amps … <br /><br />because that would happen? <br /><br />Thank you .. for your reply.<br />

  23. Hi .. Good day <br /><br />I have a question <br /><br />I have two banks of batteries and two battery chargers in parallel 48cvd <br /><br />and a total current of 35 amp, i thought that was going to of dividing the current in half <br /><br />but charger was left with 10 and one with 25 amps … <br /><br />because that would happen? <br /><br />Thank you .. for your reply.<br />

  24. I really love reading and following your post as I find them extremely informative and interesting. This post is equally informative as well as interesting . Thank you for information you been putting on making your site such an interesting. I gave something for my information. <a href="http://tipsonlaptop.com/solar-charger/&quot; rel="nofollow">Solar Charger</a>

  25. 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.

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

  27. 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 />

    • offcourse u can connect 2 150ah batteries but the wattage of the solat panel is very less to charge u r batteries for that u r inverter should charge u r batteries from main power in this case u r power bill will increase.<br /><br />2-u can charge u r batteries from direct power. but some problems due to the fluctuations occurance of sun light the voltage and ampers can be ups and downs and the

  28. 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.

  29. 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

  30. 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.

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

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