Discharge time of 12v 8.4Ah at 5mA rate












4














I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.



Anyway, I have a GPS tracker fitted with a rated consumption of 5mA. According to this formula I have to divide battery capacity by consumption:



8.4 from battery / 0.005 consumption = 1680 hours (70 days)



Is this correct? The reason why I am posting this is because the battery says 8.4Ah, which is only double as many mobile phone batteries:



Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12V? My knowledge in electronics is zero as you can see.



Thanks and happy NY!









share









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daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • 3




    To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
    – Brian Drummond
    9 hours ago








  • 2




    12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
    – JRE
    8 hours ago












  • Question title should say ...at 5mA rate, not 5mAh.
    – J...
    4 hours ago
















4














I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.



Anyway, I have a GPS tracker fitted with a rated consumption of 5mA. According to this formula I have to divide battery capacity by consumption:



8.4 from battery / 0.005 consumption = 1680 hours (70 days)



Is this correct? The reason why I am posting this is because the battery says 8.4Ah, which is only double as many mobile phone batteries:



Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12V? My knowledge in electronics is zero as you can see.



Thanks and happy NY!









share









New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 3




    To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
    – Brian Drummond
    9 hours ago








  • 2




    12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
    – JRE
    8 hours ago












  • Question title should say ...at 5mA rate, not 5mAh.
    – J...
    4 hours ago














4












4








4







I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.



Anyway, I have a GPS tracker fitted with a rated consumption of 5mA. According to this formula I have to divide battery capacity by consumption:



8.4 from battery / 0.005 consumption = 1680 hours (70 days)



Is this correct? The reason why I am posting this is because the battery says 8.4Ah, which is only double as many mobile phone batteries:



Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12V? My knowledge in electronics is zero as you can see.



Thanks and happy NY!









share









New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.



Anyway, I have a GPS tracker fitted with a rated consumption of 5mA. According to this formula I have to divide battery capacity by consumption:



8.4 from battery / 0.005 consumption = 1680 hours (70 days)



Is this correct? The reason why I am posting this is because the battery says 8.4Ah, which is only double as many mobile phone batteries:



Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12V? My knowledge in electronics is zero as you can see.



Thanks and happy NY!







batteries 12v discharge time





share









New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.










share









New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








share



share








edited 1 hour ago









glglgl

290210




290210






New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 9 hours ago









daviddgz

211




211




New contributor




daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






daviddgz is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 3




    To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
    – Brian Drummond
    9 hours ago








  • 2




    12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
    – JRE
    8 hours ago












  • Question title should say ...at 5mA rate, not 5mAh.
    – J...
    4 hours ago














  • 3




    To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
    – Brian Drummond
    9 hours ago








  • 2




    12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
    – JRE
    8 hours ago












  • Question title should say ...at 5mA rate, not 5mAh.
    – J...
    4 hours ago








3




3




To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
– Brian Drummond
9 hours ago






To explain the 10h rate, if you discharge it faster, you see less capacity. As you are discharging slowly, use the 20h rate as you have done. Your math is correct BUT assuming it's a lead-acid battery, to avoid damaging it, don't fully discharge it : it'll last better rated at 50% or 35 days. And remember it's 12V not 3.7V so its capacity is about 6-7* the cellphone battery energy capacity. That and the lead content explains the weight.
– Brian Drummond
9 hours ago






2




2




12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
– JRE
8 hours ago






12V*8.4Ah = 100Wh. 3.7V*4.2Ah=15.5Wh. Watt hours are the key, not ampere hours. Watt hours are energy - it tells you how much energy you can get out of the battery. Ampere hours are not an energy unit. Energy is power * time. Power is volts * amperes.
– JRE
8 hours ago














Question title should say ...at 5mA rate, not 5mAh.
– J...
4 hours ago




Question title should say ...at 5mA rate, not 5mAh.
– J...
4 hours ago










2 Answers
2






active

oldest

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11















I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.




The capacity decreases at higher discharge rates. The figures are telling you that discharge current of $ frac {8.4 text {Ah}}{20 text h} = 0.42 text A $ will last 20 h and $ frac {8.0 text {Ah}}{10 text h} = 0.8 text A $ will last 10 h. Given that doubling of discharge rate the total energy out is actually surprisingly close.




8.4 from battery / 0.005 consumption = 1680 hours (70 days).




Correct method. (I didn't check your numbers but they look right.)




Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12 V?




Two reasons:




  • As you suspect, the 12 V is related. The energy stored in the battery is given by $ V times I times t $ so a 12 V battery will have three times the energy storage of a 4 V battery. Your 12 V battery has a capacity of $ 12 times 0.42 times 20 = 100 text {VAh} = 100 text {Wh}$.

  • Battery chemistry. Your mobile phone battery is a lithium based battery. According to Green Transportation :


    • Lead acid energy density is 33 - 42 Wh/kg so we would expect your battery to weigh about 3 kg.

    • Lithium ion energy density is 100 to 265 Wh/kg so we could get the same energy storage in a 0.4 kg battery.




enter image description here



Figure 1. Energy densities for various technologies. Source: EPEC.






share|improve this answer































    2














    From Here:




    If a battery has a rating of 100AH @ 20Hr rate, then that battery
    was discharged over 20 hours with a 5 amp load. Starting batteries, on
    the other hand, are typically rated at 10Hr rate, because they are
    used faster, so the 20Hr rate is not as important.




    A battery has an internal serial resistance. Faster you discharge, higher are the losses, that is why they provide different capacity for different discharge rate.



    In your case since you discharge very slowly you can take the first value.



    Your formula is correct. However batteries also have a self discharge rate that you might want to consider if you need long period.




    Why this motorbike battery is so heavy then if it's only double the
    capacity? Is it because it's a 12V?




    This part isn't clear, you can edit your question and I will edit the reply.



    If it's only the double capacity of "what" ?



    You need to multiply the capacity by the voltage to know the total energy stored, so 8.4 * 12 = 100.8Wh.



    A 8.4Ah 5V battery will have less than half capacity.



    Also Lead-Acid batteries (probably what you have) are heavy and low power density. Li-ion batteries (like on the phones/laptop) have much higher power density so it will be much lighter for the same amount of stored energy.






    share|improve this answer























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      2 Answers
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      2 Answers
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      11















      I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.




      The capacity decreases at higher discharge rates. The figures are telling you that discharge current of $ frac {8.4 text {Ah}}{20 text h} = 0.42 text A $ will last 20 h and $ frac {8.0 text {Ah}}{10 text h} = 0.8 text A $ will last 10 h. Given that doubling of discharge rate the total energy out is actually surprisingly close.




      8.4 from battery / 0.005 consumption = 1680 hours (70 days).




      Correct method. (I didn't check your numbers but they look right.)




      Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12 V?




      Two reasons:




      • As you suspect, the 12 V is related. The energy stored in the battery is given by $ V times I times t $ so a 12 V battery will have three times the energy storage of a 4 V battery. Your 12 V battery has a capacity of $ 12 times 0.42 times 20 = 100 text {VAh} = 100 text {Wh}$.

      • Battery chemistry. Your mobile phone battery is a lithium based battery. According to Green Transportation :


        • Lead acid energy density is 33 - 42 Wh/kg so we would expect your battery to weigh about 3 kg.

        • Lithium ion energy density is 100 to 265 Wh/kg so we could get the same energy storage in a 0.4 kg battery.




      enter image description here



      Figure 1. Energy densities for various technologies. Source: EPEC.






      share|improve this answer




























        11















        I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.




        The capacity decreases at higher discharge rates. The figures are telling you that discharge current of $ frac {8.4 text {Ah}}{20 text h} = 0.42 text A $ will last 20 h and $ frac {8.0 text {Ah}}{10 text h} = 0.8 text A $ will last 10 h. Given that doubling of discharge rate the total energy out is actually surprisingly close.




        8.4 from battery / 0.005 consumption = 1680 hours (70 days).




        Correct method. (I didn't check your numbers but they look right.)




        Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12 V?




        Two reasons:




        • As you suspect, the 12 V is related. The energy stored in the battery is given by $ V times I times t $ so a 12 V battery will have three times the energy storage of a 4 V battery. Your 12 V battery has a capacity of $ 12 times 0.42 times 20 = 100 text {VAh} = 100 text {Wh}$.

        • Battery chemistry. Your mobile phone battery is a lithium based battery. According to Green Transportation :


          • Lead acid energy density is 33 - 42 Wh/kg so we would expect your battery to weigh about 3 kg.

          • Lithium ion energy density is 100 to 265 Wh/kg so we could get the same energy storage in a 0.4 kg battery.




        enter image description here



        Figure 1. Energy densities for various technologies. Source: EPEC.






        share|improve this answer


























          11












          11








          11







          I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.




          The capacity decreases at higher discharge rates. The figures are telling you that discharge current of $ frac {8.4 text {Ah}}{20 text h} = 0.42 text A $ will last 20 h and $ frac {8.0 text {Ah}}{10 text h} = 0.8 text A $ will last 10 h. Given that doubling of discharge rate the total energy out is actually surprisingly close.




          8.4 from battery / 0.005 consumption = 1680 hours (70 days).




          Correct method. (I didn't check your numbers but they look right.)




          Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12 V?




          Two reasons:




          • As you suspect, the 12 V is related. The energy stored in the battery is given by $ V times I times t $ so a 12 V battery will have three times the energy storage of a 4 V battery. Your 12 V battery has a capacity of $ 12 times 0.42 times 20 = 100 text {VAh} = 100 text {Wh}$.

          • Battery chemistry. Your mobile phone battery is a lithium based battery. According to Green Transportation :


            • Lead acid energy density is 33 - 42 Wh/kg so we would expect your battery to weigh about 3 kg.

            • Lithium ion energy density is 100 to 265 Wh/kg so we could get the same energy storage in a 0.4 kg battery.




          enter image description here



          Figure 1. Energy densities for various technologies. Source: EPEC.






          share|improve this answer















          I have a motorcycle battery rated as 8.4Ah (20HR). It also says 8Ah (10HR) and I am not sure what´s the difference.




          The capacity decreases at higher discharge rates. The figures are telling you that discharge current of $ frac {8.4 text {Ah}}{20 text h} = 0.42 text A $ will last 20 h and $ frac {8.0 text {Ah}}{10 text h} = 0.8 text A $ will last 10 h. Given that doubling of discharge rate the total energy out is actually surprisingly close.




          8.4 from battery / 0.005 consumption = 1680 hours (70 days).




          Correct method. (I didn't check your numbers but they look right.)




          Why this motorbike battery is so heavy then if it's only double the capacity? Is it because it's a 12 V?




          Two reasons:




          • As you suspect, the 12 V is related. The energy stored in the battery is given by $ V times I times t $ so a 12 V battery will have three times the energy storage of a 4 V battery. Your 12 V battery has a capacity of $ 12 times 0.42 times 20 = 100 text {VAh} = 100 text {Wh}$.

          • Battery chemistry. Your mobile phone battery is a lithium based battery. According to Green Transportation :


            • Lead acid energy density is 33 - 42 Wh/kg so we would expect your battery to weigh about 3 kg.

            • Lithium ion energy density is 100 to 265 Wh/kg so we could get the same energy storage in a 0.4 kg battery.




          enter image description here



          Figure 1. Energy densities for various technologies. Source: EPEC.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 6 hours ago

























          answered 8 hours ago









          Transistor

          80.6k778174




          80.6k778174

























              2














              From Here:




              If a battery has a rating of 100AH @ 20Hr rate, then that battery
              was discharged over 20 hours with a 5 amp load. Starting batteries, on
              the other hand, are typically rated at 10Hr rate, because they are
              used faster, so the 20Hr rate is not as important.




              A battery has an internal serial resistance. Faster you discharge, higher are the losses, that is why they provide different capacity for different discharge rate.



              In your case since you discharge very slowly you can take the first value.



              Your formula is correct. However batteries also have a self discharge rate that you might want to consider if you need long period.




              Why this motorbike battery is so heavy then if it's only double the
              capacity? Is it because it's a 12V?




              This part isn't clear, you can edit your question and I will edit the reply.



              If it's only the double capacity of "what" ?



              You need to multiply the capacity by the voltage to know the total energy stored, so 8.4 * 12 = 100.8Wh.



              A 8.4Ah 5V battery will have less than half capacity.



              Also Lead-Acid batteries (probably what you have) are heavy and low power density. Li-ion batteries (like on the phones/laptop) have much higher power density so it will be much lighter for the same amount of stored energy.






              share|improve this answer




























                2














                From Here:




                If a battery has a rating of 100AH @ 20Hr rate, then that battery
                was discharged over 20 hours with a 5 amp load. Starting batteries, on
                the other hand, are typically rated at 10Hr rate, because they are
                used faster, so the 20Hr rate is not as important.




                A battery has an internal serial resistance. Faster you discharge, higher are the losses, that is why they provide different capacity for different discharge rate.



                In your case since you discharge very slowly you can take the first value.



                Your formula is correct. However batteries also have a self discharge rate that you might want to consider if you need long period.




                Why this motorbike battery is so heavy then if it's only double the
                capacity? Is it because it's a 12V?




                This part isn't clear, you can edit your question and I will edit the reply.



                If it's only the double capacity of "what" ?



                You need to multiply the capacity by the voltage to know the total energy stored, so 8.4 * 12 = 100.8Wh.



                A 8.4Ah 5V battery will have less than half capacity.



                Also Lead-Acid batteries (probably what you have) are heavy and low power density. Li-ion batteries (like on the phones/laptop) have much higher power density so it will be much lighter for the same amount of stored energy.






                share|improve this answer


























                  2












                  2








                  2






                  From Here:




                  If a battery has a rating of 100AH @ 20Hr rate, then that battery
                  was discharged over 20 hours with a 5 amp load. Starting batteries, on
                  the other hand, are typically rated at 10Hr rate, because they are
                  used faster, so the 20Hr rate is not as important.




                  A battery has an internal serial resistance. Faster you discharge, higher are the losses, that is why they provide different capacity for different discharge rate.



                  In your case since you discharge very slowly you can take the first value.



                  Your formula is correct. However batteries also have a self discharge rate that you might want to consider if you need long period.




                  Why this motorbike battery is so heavy then if it's only double the
                  capacity? Is it because it's a 12V?




                  This part isn't clear, you can edit your question and I will edit the reply.



                  If it's only the double capacity of "what" ?



                  You need to multiply the capacity by the voltage to know the total energy stored, so 8.4 * 12 = 100.8Wh.



                  A 8.4Ah 5V battery will have less than half capacity.



                  Also Lead-Acid batteries (probably what you have) are heavy and low power density. Li-ion batteries (like on the phones/laptop) have much higher power density so it will be much lighter for the same amount of stored energy.






                  share|improve this answer














                  From Here:




                  If a battery has a rating of 100AH @ 20Hr rate, then that battery
                  was discharged over 20 hours with a 5 amp load. Starting batteries, on
                  the other hand, are typically rated at 10Hr rate, because they are
                  used faster, so the 20Hr rate is not as important.




                  A battery has an internal serial resistance. Faster you discharge, higher are the losses, that is why they provide different capacity for different discharge rate.



                  In your case since you discharge very slowly you can take the first value.



                  Your formula is correct. However batteries also have a self discharge rate that you might want to consider if you need long period.




                  Why this motorbike battery is so heavy then if it's only double the
                  capacity? Is it because it's a 12V?




                  This part isn't clear, you can edit your question and I will edit the reply.



                  If it's only the double capacity of "what" ?



                  You need to multiply the capacity by the voltage to know the total energy stored, so 8.4 * 12 = 100.8Wh.



                  A 8.4Ah 5V battery will have less than half capacity.



                  Also Lead-Acid batteries (probably what you have) are heavy and low power density. Li-ion batteries (like on the phones/laptop) have much higher power density so it will be much lighter for the same amount of stored energy.







                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited 8 hours ago

























                  answered 9 hours ago









                  Damien

                  2,132315




                  2,132315






















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