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Rechargeable battery charging time vs. mA current calculator

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NiMH & NiCd rechargeable batteries charging time – mAh – mA / hours :

Step 1: Enter a mAh capacity of your Rechargeable Battery

* Enter a mAhr capacity value as shown on one battery only (to charge 1 to 4 batteries at once.)
* Precision in results is how many numbers after decimal point (0 – 9)

Enter a mAh number of your battery : (ei: 2400) mAh   –   Precision :

Step 2: Select a rechargeable battery size/type to calculate from

Step 3: Select battery charger mA current output rate for time length


Battery size, charging time length, charger current output type.

How long time does it take to recharge a rechargeable battery?

Formula for calculating batteries charging time :

hr = mAh / mA

hours” equal “battery size in milliampere-hour” divided by “charger output power in milliamperes

(Need more information? The charge formula is explained in details with examples further below.)

Charging rechargeable batteries.

Type into the calculator your rechargeable battery’s capacity number, normally can be red on the battery body e.g. 1700 mAh ( milli-ampere-hours ). Then select the battery type/size in the left column ( NiMH – NiCd – AAA – AA – C – D – 9V ( 9 volt )) and in the right side select a current output ( electric power output ) of your charger in mA ( milli-amperes ).

Type in a capacity number of one battery only. Without changing outcome as per hours/mA a 1-4 batteries can be charged.

You can select and use a specific / special battery sizes at the bottom of the field and then set a different current output from a battery charger, if needed, by choosing the 1mA current and multiplying the outcome backwards – dividing in fact by the existing current value at which your charging equipment operates.

Re-charging 9 volt rechargeable batteries

Time control for charging of common 9V rechargeable batteries ( NiCd and NiMH 9 V batteries.) The timer takes longer because these can only be charged at much lower current rate of 0.1C or 1/10C ( mAhr/10 = charging time in hours ) of their mAh capacity value. Usually between 30 mA to 100 mA depending on the 9V battery capacity in mAh. This is still great to put up with considering that the 9 volts non rechargeable batteries cost arm and leg, but they don’t have to.

Trickle charge, continuous charging method

This is done with a very low charging current to keep the battery or batteries constantly alive, same like with a cordless phone battery pack that is docked in its station base.

Lets do the life/live charging examples, but before still in a short theory to clear some practical terminology out from the way.

Common abbreviations – symbols – prefixes

The International acronyms one will possibly come across with while using batteries and their changers:

How do I calculate charging time for rechargeable battery manually ?

Formula for manual calculation for battery recharging processes

AAA – AA – C – D sizes rechargeable batteries:
hours ( charging time ) equals to 12 x Ahr = hrs OR 12/1000 x mAh = hrs
( 12/1000 x mAh = hours of charging )

Example calculations with this manual formula; calculate charging time length for 2400 mAh NiMH AA size 1.2v rechargeable batteries with 100 mA charger and secondly with a 3.5 times more powerful 350 mA current output power charger:

100mA battery charger:
12 : 1000 = 0.012
0.012 x 2400 = 28.8 (hrs)

It requires 28.8 hours ( 28 hours and 48 minutes ) to charge or recharge aa size 2400mAh batteries with charger that has 100mA current output.

350mA battery charger:
12 : 1000 = 0.012
0.012 x 2400 = 28.8
28.8 : 3.5 = 8.2 (hrs)

It takes 8.2 hours ( 8 hours and 12 minutes ) time to charge or recharge 2400mAh batteries with charger that has 350mA current output.

Here is a second example of how long to charge batteries but this time for charging 1800 mAh 1.2 volt NiMH aa type rechargeable batteries and with the same current chargers:

100mA battery charger:
12 : 1000 = 0.012
0.012 x 1800 = 21.6 (hrs)

It takes 21.6 hours ( 21 hours and 36 minutes ) to charge or recharge aa size 1800mAh batteries with charger that has 100mA current output.

350mA battery charger:
12 : 1000 = 0.012
0.012 x 1800 = 21.6
21.6 : 3.5 = 6.2 (hrs)

In total 6.2 hours ( 6 hours and 12 minutes ) is needed to charge or recharge 1800mAh batteries with charger that has 350mA current output power.

9v ( 9 volt ) rechargeable batteries:
hours equal to battery mAhr/10 ( mAh/10 = hrs )


battery charging time = capacity of the battery / charging current power output of the charger

hr = mAh / mA

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  1. I have Lithium Ion 3.7V nominal voltage, 9.6Ah Nominal Capacity, recommended 1.6 A battery. How long should I keep it on charge and how much does it cost to charge per hour? It is for my battery bicycle.

    Comment from/about : Sharon | Permalink

  2. Sharon,
    Thank you for your comment. A battery bicycle?! Great, I would like to be more specific and reply in detail including the cost per charge or per hour; but could you please input more information I need?

    What are the charger parameters and also any info on what the manufacturer suggests.

    What are the lithium battery technical data – should I assume the numbers relate to the battery only. I can be more specific if I had:
    – no “Vdc” number is mentioned, as in nominal charging voltage and at some +, – of few degrees temperature?
    – put separately the Nominal Voltage of your Lithium Ion Battery and specs of the Charger For This Battery?

    Could you provide photographs of both the battery and the charger you are supposed to use, to charge it with?

    Comment from/about : Rado | Permalink

  3. can i charge my rc car 9.6V 3000 mAh battery with a 9V 850 mAh adapter? if yes how long should it take? my rc car has a 2 x 9.6V 3000 mAh NiCd battery and can i replace 1 of the battery pack with a 9.6 V NiMH 4200 mAh which means 1 x 9.6 V 3000 mAh + 1x 9.6V 4200 mAh NiMH battery to operate?

    Comment from/about : jeff | Permalink

  4. I am confused if this chart is referring to the individual cells within a battery pack or the total of the battery pack. I have a 4 cell AA 400mah 4.8v battery pack for a small radio controlled boat. The charger supplied is 250 mah. That is all the information provided on the outside of the battery pack/charger. How long should it charge at that rate to be fully charged? I do not wish to over charge as I understand you risk a problem of exploding batteries etc.


    Comment from/about : Indy | Permalink

  5. Indy, yes correct overcharging batteries or incorrect charging technique might damage them more than just lower/shorten their life span and you do not want that to happen surely. this is easy; when batteries are connected in series, the capacity remains constant while voltages add. Whilst with the parallel connection of batteries, voltage is constant but capacities add. Is that 4.8 volts battery pack put together from four 1.2 volt NiCd batteries type ( nickel–cadmium battery or NiCad battery) or the NiMH batteries type ( nickel–metal hydride battery or Ni-MH ), can you specify this? The intention is to charge them in the set pack in series 4.8v right? ( all 4 batteries connected plus to minus ) Or in parallel? ( e.g. disconnected from series connection, charging each battery separately, but all four together at the same time at 1.2v each )

    Comment from/about : Rado | Permalink

  6. Dear friends

    I want your help in order to complete my solar light project.

    I have a li-on battery of 3.7 at 2300mah that is needed for the led lights.

    My question is the following.

    What kind of solar cell i need to have (cell’s voltage and wattage) in order to recharge the battery correctly during the day light?

    I have to inform you that the amperage that the led lights have as a load is approximately around 150mah.

    Thanks in advance and best regards.

    Comment from/about : Stefanos Konstantopoulos | Permalink

  7. Is it OK to charge a 12v drill battery with a 18v 0.7A charger? It’s A NI-CD 1200mah cordless drill BATTERY. If so, how long will the charging process take please?

    Comment from/about : cliff | Permalink

  8. Can I upgrade my 9.6 volt 1000 mAh battery to a 9.6v 1600 mAh ni-cad in a RC car ?

    Comment from/about : Chester | Permalink

  9. I do not see any reason as to why couldn’t the battery be exchanged for the one with a higher capacity in milli ampere hours. It is only matter of mAh increase by 600mAh units whilst at this time it maintains equally same battery voltage. It is not a voltage change therefore there should not be an obstacle for the battery upgrade.

    Comment from/about : Rado | Permalink

  10. Can I replace my 1100mAh Canon battery with a 1700mAh? It has the same volts just higher mAh – want to make sure it will work in my camera before ordering.

    Comment from/about : Ann – battery replacement | Permalink

  11. Ann, certainly the battery can be replaced from the 1100 mAh for the one with higher 1700 mAh power storage capacity. It will hold the power charge for longer when in use.

    Comment from/about : Rado | Permalink

  12. Does this Charge Calculator base its output charge times on the batteries in question being at a zero state of
    charge or are the Charge Times listed for a given battery the same regardless of how much charge remains in
    the battery at the time they are put in the Battery Charger?

    I ask this because I’m using a 250 mA charger and at the time I put my batteries in my charger, most of them
    still have one-half or more of their total 1.2V charge still in them.

    Within a half hour I can put my volt meter on them and they’ll read 1.35-1.37 V. I’m afraid if I leave them in
    any longer they’ll over-charge to the point of ruin. (which I may have already done based on several dead
    batteries that no longer hold a charge.

    Other than this confusion on my part, I really found this calculator helpful. Thanks for your help.

    Comment from/about : What State of Discharge | Permalink

  13. A while back I damaged 4 near new batteries by not switching between NiCd and NiMH on the charger. And that hurts as they were the better quality kind.

    The voltage 1.35-1.37 V does not really say the battery capacity potential is already reached. From this volts reading, the charging process can take another ~70% of the whole charging time.

    Are you able to fully discharge your batteries and then fully charge them all together? This is the preferred method. Also, what type of batteries are they? A charger can first drain batteries completely at the beginning and only then start charging to 100%.

    Here to your question; not just occasionally I use a different travel charger, while each of the batteries is not equally discharged, I simply charge them at that state as they are. Later on at home, my main charger discharges them and then charging goes on, which fixes their memory to normal (if they are smart.) A few of my batteries I’ve been using for 5+ years without any problem. This way, those bad ones MIGHT be fixed, so worthy to try.

    Another thing I do, batteries which aren’t charged anymore enough for a torch and radio for instance, I do not charge them yet. First I place them into a TV or video remote control. When they stop working there, then I use charger. It’s just a very quick and practical routine!

    Comment from/about : Rado | Permalink

  14. Please help me. I have a battery charger on which the information given is power INPUT: AC 220v 50Hz, OUTPUT: DC 1.4V and I have rechargeable battery of 2100mah, 1.2v which I bought new, so can you tell me how much of time in hours will it take for the first time recharge for 2 of these batteries at a time?
    Thank you very much in advance.

    Comment from/about : somi | Permalink

  15. Hello Somi,
    Could you supply 3 additional kinds of information for charging those batteries in twos, as the needed info is missing.

    1. is it a charger which charges the 1.2 volts batteries in pairs – 2 batteries at the time

    2. what is the charger’s output in milliampere [mA] – e.g. 400 mA or 210 mA etc., if it has different milliampere numbers mention them all), also is it NiCd or NiMH type and is it a rapid charger?

    3. what battery type are they, NiMH or NiCd and the size AA or AAA?

    Comment from/about : Rado | Permalink

  16. I have a RC helicopter but the battery it uses takes forever to charge and then allowance is approximately 10 minutes time of flight consequently having have to recharge the battery again and again. The battery specs are 3.7v lithium polymer battery plus draws 150mAh power. My question is if I buy a 3.7v with a larger amount of mAh for instance 2000mAh with the same voltage plus type and size, will I generate an increase in the actual usage time without damage to the el. motor on this remote controlled electric helicopter?

    Comment from/about : Lithium Polymer | Permalink

  17. How long time does it take to discharge a rechargeable battery in question.
    Specifications of the battery:

    600 mAh power output – usage 0.5 Watt

    Comment from/about : krishna | Permalink

  18. I have developed a charging ckt that I can set the charging current to any value from 160ma to 1 amp. At 1 amp my circuit shuts down in 5 minutes and disconnect the batteries from the charger. All the batteries test good on a load tester. I can with these set up conditions, charge several 1.2V batteries in series. Question: Is one amp to much for recharging?

    Comment from/about : Vince | Permalink

  19. I have (3.6V, 8.74mA DC) harvester, and I want to calculate the time to charge a battery (AAA 800mAh, 1.2V)
    After charging I found every 10sec it charges 1mV, how many days do I need to charge the battery fully by using that harvester?

    Thank you and warm regards

    Comment from/about : Battery charging Energy and time | Permalink

  20. What kind of energy harvester do you have, is it a circuit or something simpler or more advanced? Anything renewable? That is interesting concept.

    If it produces 3.6 volts constant, do you intend to connect these 3x 1.2 volts 800 mAh AAA batteries in series? Let me know, I could calculate the numbers for this.

    Comment from/about : Rado | Permalink

  21. Vince,
    Do you mean 1 amp for 1.2V D, AAA or AA rechargeable batteries? What sort of circuit do you have (“ckt”) with what sort of output?

    Comment from/about : Rado | Permalink

  22. I’m looking if you can help me in charging me batteries with automatic charger schematic circuit that could charge 3xAA 1200 mAh batteries with monitoring leds during the charging time, but when the charging time is over it should cut off but always stay on line reading status of the batteries, for example when the batteries in the charger need to be recharged it should be done fully automatically.
    Awaiting your prompt action. g752
    Thanks in advance.

    Comment from/about : NiCd automatic charger | Permalink

  23. This is GREAT stuff! I was hoping a website like this for charging times would exist. I found the information on the battery and on the charger and it told me it’s 13h. THANK YOU!

    Comment from/about : Jaxx | Permalink

  24. The information this page provides is extremely helpful to me as I have quite a large variety of different rechargeable type batteries to charge. Also I find building my own specific chargers to be a lots of fun. I have been using LM317 etc. and proper resisters to get always the correct charging current. I use this C/10 formula for the program. I never rush any charging time. Thank you very much for putting this web page together.

    Comment from/about : David Connolly | Permalink

  25. I am in desperate need of a NI-MH Battery Pack
    Model BT 1028 3.6V-550mAh
    Do you have them or know where I can purchase these batteries? It has to be the exact power BT1028 3.6V – 550mAh pack model and for multiple recharging of course.

    Comment from/about : Rose | Permalink

  26. Greetings,
    I have 2 lie on rechargeable batteries (18650, 6800mAh 3.7 volt dc) and a charger that has specs of … Input 100-240 volt AC MAX 150mA, Output 4.2 v doc 450 mA, No Load Power Consumption: 1 watt MAX, Full Load Power Consumption: 7 watts MAX, Battery Charge Rate 80%. My question is….. Will this charger fully charge the batteries to there full potential?
    Thank you, KTS 🙂

    Comment from/about : KTS | Permalink

  27. They seem to be a high quality batteries. Although the charger specs show the charger might be weak to charge them to the batteries’ fullest potential plus its voltage output level would not fit too well. For the time being it could work.

    Comment from/about : Rado | Permalink

  28. I’m charging my phone internal lithium ion battery with 890mah output current but the phone heats up so much does the charger I should carry or go for a new one???

    Comment from/about : utkarsh | Permalink

  29. The battery AA-AAA charger with about 50-70 mA or so is good.

    Comment from/about : Douglas Fleshman | Permalink

  30. I have a Minelab Slimpack nimh rechargeable battery pack-9.6v 1600 mah The charger has 110v ac 60hz input and 15v dc 100ma Can you please tell me how long this battery pack should be charged? The charger is a AC/DC ADAPTER.

    Comment from/about : Ron | Permalink

  31. Having 2,800 mah rechargeable batteries but didn’t now how long to charge them with my charger of DC 2.8V

    Comment from/about : Sean | Permalink

  32. This calculator does not give a correct result. I think this is because of a stray multiplier you introduced in one of the formulas you use.

    You state the theoretical formula for calculating the time it would take to charge (given that charging commences without losses at a constant current):

    “hr = mAh / mA”

    But then you introduce a multiplier in this formula that adds 20% to the intended charge level and respectively to the charge time:

    “hours ( charging time ) equals to 12 x Ahr = hrs OR 12/1000 x mAh = hrs ( 12/1000 x mAh = hours of charging )”

    And all your calculations after that are theoretically wrong (20% above what should be the right theoretical answer). So, my question is “Where did that 12 come from? What does it represent? If `12 x Ahr = hrs`, then it follows that the unit `12` is in is A^-1 (Ampere to the power of -1).”

    You can check your calculator by setting the capacity to 100 mAh and the charger current to 100 mA. This should give you 1 hr, but your calculations point at 1.2 hr -> 20% more than should be theoretically expected.

    Comment from/about : Pavlin | Permalink

  33. Awesome boss!

    Comment from/about : DANISH | Permalink

  34. Pavlin,
    Please note that the formula “hr = mAh / mA” represents only the logic of the practicality. It needs to go further.

    The charging current 1.2A needs to be applied like so:

    12 x Ahr = hrs OR 12/1000 x mAh = hrs ( 12/1000 x mAh = hours of charging time )

    It is the charging current which is 1.2 Amperes.

    But do not confuse this 1.2 amperes charging current number with ampere-second (the coulomb unit) or the ampere-hour. Even though the Ampere is actually a SI unit of current being transited per unit-time. In other words; transiting current is the ‘ampere unit’, and, the other ‘ampere-second or ampere-hr is a unit of charge’).

    A. The ampere-second and ampere-hour are units of charge.

    B. The ampere is a unit of current.

    The relation of of the coulomb to the ampere (C/s) is like with the relation of the joule to the watt (J/s).

    An average, instantaneous and constant current are expressed in Amperes (e.g. the “charging current comes to 1.2A”) and the charge passed through a circuit over some length of time or the charge accumulated in battery is expressed in coulombs (e.g. the “battery charge comes to 30,000 Coulombs”.)

    Comment from/about : Rado | Permalink

  35. How to calculate life time of rechargeable battery? How many years a rechargeable battery can work?

    Comment from/about : Nirmitee | Permalink

  36. I noticed that your calculator differentiates between NiMH and NiCd batteries. Which must be correct probably, NiMH versus NiCd are different technology and systems. Also, the charging time calculated is varies depending on which battery type is selected. I’ve read and re-read this page and other similar pages and can’t figure out why there is a difference. Can you share the formula for calculating charging times of NiCd vs the one for NiMH? Thank you for your time.

    Comment from/about : NiMH vs NiCd charging time | Permalink

  37. NiMH and NiCd batteries are simply produced of totally different material. By chemistry and physics. That is why the charging structure influence differs. Battery charges are built accordingly with these in mind, by design they can be switched to NiCd or to NiMH options.

    NiMH refers to Nickel Metal Hydride material and NiCd refers to Nickel Cadmium material.

    Comment from/about : Rado | Permalink

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