BU-1004b: How to Calculate Battery Capacity

Everyone wants a battery that is small and light, but there are compromises, especially if the margin for failure is narrow for critical missions. When calculating battery size, the fleet user should consider two factors: [1] allowing for spare capacity to provide for unforeseen activities, and [2] anticipating capacity fade that occurs naturally with the age of the battery. Equipment manufacturers tend to ignore the fading aspect when calculating the required capacity and base the service on a new battery with full capacity.

The acceptable capacity performance range of a well-managed battery fleet is 80 to 100 percent, meaning that packs that fall below the 80 percent threshold are replaced. Allocating 20 percent fade in addition to a 20 percent emergency reserve would reduce the usable battery capacity to 60 percent. Such a large reserve for a worst-case scenario may not be practical and battery users go for more leniency. A battery analyzer plays an important role in battery management in that the batteries are checked every one to thee months to ensure they all fall within the anticipated performance bandwidth. 


On April 23, 2011 at 3:07am


On July 4, 2011 at 4:30am
Adrian Smit wrote:

We are trying to locate the best battery for a vehicle tracking device, the battery needs to be a small as possible, have no charge source once it has been full charged our devices are not hot wired into the vehicle the device needs to live on its own battery for as long as possible. Our devices don’t have any LED lights or battery drawing components other that the GPS and GSM modules. Can you suggest the right battery for us.

Regards Adrian Smit.

On September 25, 2011 at 11:46am
satyendra wrote:

hi every one…
ageing of batteries matters for calculating the capacity. like when cells are new, it has 100% capacity but as time passes and usage cells goes on capacity decreases…so how to know exactly what is the fraction of capacity reduced while using.

On October 14, 2011 at 8:38am
mahmood wrote:

hello SM TAHIR HUSSAIN! im MBA student of PAF-KIET doing my finance elective course of financial modeling & forcasting for this i have selected atlas battery to work so i need a company contact person to have a quality output so please allow me to contact with you, your support will be a great addition to my study report!

looking forward for your kind support!

im available at email: mahmoodsofur@gmail.com

On December 13, 2011 at 8:26pm
chris king wrote:

We are trying to figure out the best size and type rechargeable battery to use in our solar light.  It currently is set up with 4 aaa’s.  it is trickle charges with a 5-6V solar panel.  Any thoughts?  Some say low mA ni-cads, others nmhi.

On March 16, 2012 at 6:35pm
Michael Mc Cann wrote:

I am designing an off-grid solar electric system for domestic use.  Based on 16.6 KW/day use, 5hours of direct sun/day and a 3.8KW PV array located 100’/30m from the battery pack. Any ideas on battery size/quantity/volts?


On March 26, 2012 at 4:04am
Deepak chaudhary wrote:

i am interested in designing battery for electric vehicle can oyu let me know design formulas?

On March 28, 2012 at 1:04am
ssempijja michael wrote:

I Thank you for the great job you’re doing in availing such credible information,are there non
lead acid batteries to a tune of 180 amp hrs that can effectively be used in MBT(Tanks).
Best regards:

On April 29, 2012 at 12:35pm
Syed Muhammad Tahir Hussain wrote:

Dear Satyendra,

I am Tahir Hussain from Karachi, Pakistan and i am working Atlas Battery Limited.
I read you comment about “aging of battery matters for calculating the capacity”.
Battery Aging and Capacity are the two different things and we can not calculate battery life from its own capacity.
(1) Battery aging mean , battery life. We always calculate battery life in cycles. One discharge plus one recharge equals one cycle . Battery cycles depend on battery size , capacity, electrolyte volume , plate surface area and etc. Some small batteries have short life (less cycles) example 800 cycle. Some batteries have large cycles 5000 cycles( its also depend on vehicle running).( You can see JIS standard )
(2) Battery capacity means the ability of a fully charged battery to deliver a specified of electricity (Amp-Hrs) at a given rate (A) and period of time (H). When both numbers multiply each other its called battery capacity and its symbol AH.  Example a battery which delivers 10 amps for 10 hrs that means 100 AH.

Best wishes,

On September 14, 2012 at 8:44am
syedkaramathali wrote:

marvelous ,great information sir.

On March 9, 2013 at 9:38am
amrendra wrote:

how many time required to discharge of 12v battery of 5ohm resistor

On June 4, 2013 at 1:05am
angelin wrote:


        I having 3.6v li-ion rechargeable battery.I also using one one charger IC,this charger IC having 600mA capacity.And my li-ion battery having 45mAh.Then how can i calculate battery capacity.Pls suggest me.

On August 17, 2013 at 6:19pm
Babul reddy wrote:

Hi This babul,

I’M Working Ship Yard Company

How to calculate Battery Capacity?

Do have any formula

Because our yard Installed   Main Engine (QSK60M, 2300BHP, 1900Rpm) = 2 No’s
                                Diesel Generator 265KW = 3 No’s
So How Much Capacity of battery’s required ( Each one Engine and Each one generator)
How much Starting Torque? 

On December 1, 2013 at 7:46am
Nitin Rao Chandavar wrote:

What is the formula for calculating Battery Capacity for a given Starter Motor Capacity.  Very kindly request you to please let me have the details by mail please…..  Thanks & Best Regards, Nitin Rao Chandavar

On December 27, 2013 at 10:58am
Victor Villasenor wrote:

Is there a way to add up the c rating (discharge rate) of a lipo battery.
I know how to increased the current of two batteries ( connected in parallel)
I also know that by placing two lipo batteries in series I add up the total voltage.
what about the discharge rate ( C ).
Very kindly request your info. by email. have a nice day.

On April 10, 2014 at 2:23am
Richard Biegel wrote:


I am struggling to identify the best battery to install in my car to run a portable fridge (draws 6A) My research indicates I need what is called a deep cycle battery and one that has a high antimony to lead ratio. Also, it must be heat “resistant” as it will be fitted inside the engine compartment.

Please give me your views

Many thanks


On April 15, 2014 at 2:04pm
Mark Dumont wrote:

Consider using the Odyssey brand battery. This uses TPPL (thin plate pure lead) technology. Very good deep cycle ability. Good temp resistance. Can fit under hood just fine. Similar types of this battery are used on military vehicles.

On July 2, 2014 at 8:01pm
Madipatla wrote:

There are various calculator for Lead Acid etc but not able to find calculator for Li-ion batteries.

Any suggestion please

On September 9, 2014 at 10:38pm
balaprasadgunana wrote:

we had 2 batteries in air compressor model CFM 300 , but some bodies theft that batteries . I don’t know how to calculate and how to take that type of capacity batteries