BU-105: Battery Definitions and what they mean

Understand the differences in chemistries and ratings and how they apply.

Batteries are specified by three main characteristics: chemistry, voltage and specific energy (capacity). A starter battery also provides cold cranking amps (CCA), which relates to the ability to provide high current at cold temperatures.


The most common battery chemistries are lead, nickel and lithium, and each system needs a designated charger. Charging a battery on a charger designed for a different chemistry may appear to work at first but might fail to terminate the charge correctly. Observe the chemistry when shipping and disposing of batteries as each chemistry has a different regulatory requirement.


Batteries are marked with nominal voltage; however, the open circuit voltage (OCV) on a fully charged battery is 5–7 percent higher. Chemistry and the number of cells connected in series provide the OCV. The closed circuit voltage (CCV) is the operating voltage. Always check for the correct nominal voltage before connecting a battery.


Capacity represents specific energy in ampere-hours (Ah). Ah is the discharge current a battery can deliver over time. You can install a battery with a higher Ah than specified and get a longer runtime; you can also use a slightly smaller pack and expect a shorter runtime. Chargers have some tolerance as to Ah rating (with same voltage and chemistry); a larger battery will simply take longer to charge than a smaller pack, but the Ah discrepancy should not exceed 25 percent. European starter batteries are marked in Ah; North America uses Reserve Capacity (RC). RC reflects the discharge time in minutes at a 25A discharge. (See BU-904: How to Measure Capacity.)

Cold cranking amps (CCA)

Starter batteries, also known as SLI (starter light ignition) are marked with CCA. The number indicates the current in ampere that the battery can deliver at –18°C (0°F). American and European norms differ slightly. (See BU:902a: How to measure CCA; see BU:1102: Abbreviation under CCA)

Specific energy, energy density

Specific energy, or gravimetric energy density, defines battery capacity in weight (Wh/kg); energy density, or volumetric energy density, reflects volume in liters (Wh/l). Products requiring long runtimes at moderate load are optimized for high specific energy; the ability to deliver high current loads can be ignored.

Specific power

Specific power, or gravimetric power density, indicates loading capability. Batteries for power tools are made for high specific power and come with reduced specific energy (capacity). Figure 1 illustrates the relationship between specific energy (water in bottle) and specific power (spout opening).

Specific Power Energy Density

Figure 1: Relationship between specific energy and specific power.
The water in the bottle represents specific energy (capacity); the spout pouring the water govern specific power (loading).

AA battery can have high specific energy but poor specific power as is the case with the alkaline battery, or low specific energy but high specific power as with the supercapacitor.


The C-rate specifies the speed a battery is charged or discharged. At 1C, the battery charges and discharges at a current that is on par with the marked Ah rating. At 0.5C, the current is half and the time is doubled, and at 0.1C the current is one-tenth and the time is 10-fold. ( See BU-402, What is C-rate? )


A load defines the current that is drawn from the battery. Internal battery resistance and depleting state-of-charge (SoC) cause the voltage to drop under load, triggering end of discharge. Power relates to current delivery measured in watts (W); energy is the physical work over time measured in watt-hours (Wh).

Watts and Volt-amps (VA)

Watt is real power that is being metered; VA is the apparent power  that is affected by a reactive load. On a purely resistive load, watt and VA readings are alike; a reactive load such as an inductive motor or fluorescent light causes a phase shift between voltage and current that lowers the power factor (pf) from the ideal one (1) to 0.7 or lower. The sizing of electrical wiring and the circuit breakers must be based on VA power. (See also BU-902: How to Measure Internal Resistance.)

State-of-health (SoH)

The three main state-of-health indicators of a battery are:

  1. Capacity, the ability to store energy
  2. Internal resistance, the capability to deliver current, and
  3. Self-discharge, reflecting mechanical integrity and stress-related conditions

Li-ion reveals SoH in capacity. Internals resistance and self-discharge stay low under normal circumstances. SoH is commonly hidden form the user in consumer products; only state-of-charge (SoC) is provided.  (See BU-901: Fundamentals in Battery Testing)
SoH is sometimes divided into:

Note: Unless otherwise mentioned, RSoH refers to SoH. 

State-of-charge (SoC)

SoC reflects the battery charge level; a reading battery user is most familiar with. The SoC fuel gauge can create a false sense of security as a good and faded battery show 100 percent when fully charged.  
SoC is sometimes divided into:

Note: Unless otherwise mentioned, RSoC refers to SoC. 


State-of-function (SoF)

SoF reflects battery readiness in terms of usable energy by observing state-of-charge in relation to the available capacity. This can be shown with the tri-state fuel gauge in which the usable capacity is reflected as stored energy in the form of charge (RSoH); the part that can be filled as empty and the unusable part that cannot be restored as dud. SoF can also be presented with the fishbowl icon for a battery evaluation at a glance. Tri-state fuel gauges are seldom used in fear of elevated warranty claims. Some devices offer an access code for service personnel to read SoF.

Figure 2 summarizes battery state-of-health and state-of-charger graphically.

Stored energy
Figure 2: Relationship of battery state-of-health and state of charge.


SoH State-of-health. Generic term for battery health. Capacity is leading health indicator.
ASoH Absolute state-of-health of a new battery.
RSoH Relative state-of-health relating to available capacity
SoC State-of-charge. Generic term for charge level.
ASoC   Absolute state-of-charge of a new battery
RSoC Relative state-of-charge; charge level with capacity fade.

Last Updated 2017-11-23


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Comments (54)

On April 24, 2011 at 12:48am
Richard Sergeant wrote:

Power is always V.I. cos.f.  Can cos.f, the phase angle, be other than unity for power supplied by batteries?

On August 5, 2011 at 4:50am
Mr Varrie Adamson wrote:

I have a BT5500 Freelance Phone with 550mAh batteries - I have had problems finding same to replace. Can I use 900mAh instead?

On August 9, 2011 at 8:54pm
Dave Anderson wrote:

Electromotive Force is expressed in Volts. It is not a load.

On August 13, 2011 at 4:16pm
Alex wrote:

Mr Adamson,
as long as voltage and battery type are the same a higher mah rating is fine, as it means it will just last longer. A 900mah battery will last nearly twice as long as 500 mah.
So yes if its correct type get that one!

On October 15, 2011 at 5:10am
sharmila wrote:

require updates from battery

On October 15, 2011 at 5:11am
sharmila wrote:

what’s the difference between capacity and specific capacity

On October 16, 2011 at 11:49am
jackie wrote:

Have added my comments a few moments ago. How should i search to find out what units i can use my existing but undefinable battery on? (identification info is the battery adapter, 0801S model number D12-03A.  I tried to translate your ‘battery identication’ from your Univserity info., but to no avail - all slipped right over my head.  I’m asking for a few search steps and or shortcuts so I may learn where I may plug this adapter into rather than simply tossing it out & tomorrow find out maybe that was the adaptor I required.  thank you I’ll wait to read youjr email.

On October 27, 2011 at 6:19am
Muruhan wrote:

Sharmila, Specific capacity is not discussed in this page with respect to battery.

On February 1, 2012 at 6:04pm
De wrote:

I read through all the comments and they are useful. Thanks to all

I also have 12V 4Ah battery for the alarm system. I did not read the label before buying new one on ebay and I already bought 12V 7Ah and can not return. According to Alex I can use the 7Ah as long as it is the same Voltage.

Question is can my system charge this higher 7Ah battery?

On May 16, 2012 at 7:46am
Ron wrote:

Theoretically, the only problem would be that the amount of time it would take to charge the higher Ah battery would be greater, since the charging circuite would be supplying the same current as before. i.e. if the charging circuit supplies say 1A, it would take 4 hours to charge your old and 7 to charge your new battery.
However, it is my personal experience that when a charging circuit is designed for a lower capacity battery, a higher capacity battery does not charge as properly. But i am still investigating why that is, and i think it is due to a voltage mismatch between the charging circuitry required for the two different batteries.
Anyway, i realised now from your comment’s timestamp that my answer is now redundant.

On May 23, 2012 at 4:11pm
larry wrote:

Minor error on this page under “Load”.  The Volt is the unit of Electromotive Force (EMF).  It is a measure of the motive force that drives current through a load.  The unit of current is the amp.  Of course, basic OHM’s law applies at DC ie.,  E=IR.

On November 4, 2012 at 12:14am
Peter R trevallion wrote:

As a complete novice of solar and wind generating low voltage power, I find that the pages on your internet site are an invaluable source of information for me.
Many, many thanks.


On November 29, 2012 at 6:36pm
Bee Tee wrote:

I have need to replace Golf Buggie 2x12 volt 75ah deep cycle batteries for which I am being asked £460:
I have found web sites offering similar spec batteries for half that price. Do you think there are quality differences which justify buying the higher price ones?
I have zero knowledge of this subject and am learning from your interesting site -Many thanks -BT

On December 3, 2012 at 8:42pm
Pratik wrote:

I am planning to buy a mobile, but the cell gives less back up. Other features are perfect.
What will happen if i replace the battery by increasing just the Amphere of the cell, keeping voltage constant.

On December 29, 2012 at 3:25pm
Terri wrote:

I am trying to find the smallest battery needed for my waverunner to only charge my cell phone, GPS and wireless speaker. Can you tell me the best battery I would need? -Thanks TL

On October 13, 2013 at 2:37am
Govind Menon wrote:

I bought a 5600 mah mobile power bank. I use a Nexus 4 which has a 2100 mah batter. So ideally the power bank should be able to recharge my phone twice over from 0% but it is not. Is there some physics behind why this is happening or is it a problem with my power bank? Please help in understanding!


On October 14, 2013 at 8:47am
AndyH wrote:

Hi, I was wondering if anyone could provide a citable reference that explains the difference between float and trickle charging. Wikipedis seems to confuse the two, as do many others.

On October 17, 2013 at 6:38am
Muruhan wrote:

Govind, Simply telling, transferring the complete charge of the 5100mAh battery to charge, say, two 2550mAh batteries fully, means working against the potential barrier. Beyond a level, the potential of the bigger battery drops so low that it cannot charge the smaller battery any further. Hence, you cannot transfer the charge of the power bank completely to other batteries.

On October 17, 2013 at 10:15pm
Young Robs wrote:

Good day. i just needed to ask a question. is it compatible for a charger with this output: 4.75V—0.55A to charge a 3.7v—5.55Wh battery? thanks

On April 17, 2014 at 11:08am
Daniele UDEL wrote:

I have a doubt regarding Battery power ratings. I am currently looking at batteries for distributed generation with (real) power in the range of 50 kW.
I have noticed that manufacturers do not specify the A (amperage) at which the power rating is calculating.
Obviously I can estimate the A (amperage) implicit in the power rating by dividing power by voltage, but I was wondering if there is an industry standard for the power rating of a battery. Is it calculated at the maximum possible A? Is it calculated at C1?
Thanks for any clarification

On May 13, 2014 at 8:47am
abraham wrote:

i have a samsung battery with 3.7v 5.55wh 1650ma, can i charge this one with my usb charger ac 100-240 50/60hz 120mah dc5.0v 500ma

On March 26, 2015 at 11:02am
David wrote:

Is it true that a battery like those called OPzS can have capacity like 2V3000Ah per cell? If this is true, can this battery type have a life span of up to 15 years with minor acid maintenance under 20 degree C? All these specifications look suspicious, although, I know and have seen some of this type of batteries used in telephone exchanges.

On April 14, 2015 at 11:56pm

I want to use two 12v dc fans from solar panels how much battery i will use. Someone show me right specification of battery and specs of solar panel thanks

On May 3, 2015 at 9:16am
santhu wrote:

can i use 3000 mah battery on my phone which comes with 1500 mah battery.

On May 5, 2015 at 12:20pm
Isaiah wrote:

When purchasing an item that uses 1.9 amps and runs on 12 volts, can I buy a battery that is 12 volts but 1.4 amp hours

On May 5, 2015 at 12:23pm
Josh wrote:

If I have a bilge pump that runs on 12 volts and 1.9 amps, can I buy a battery that has 12 volts but only 1.4 amp hours and still have the bilge pump work

On May 8, 2015 at 6:56am
Rekkha wrote:

A computer ups battery is 7ah, can I replace this to 35ah car battery instead, friend told me, can see Diwali crackers at home, can I go ahead, or not, anyone pls help, intention is to increase the backup time, not the load, also one xtra car battery lying around, why paying 1000 for new7ah battery, plz help seniors, I don’t want to damage my ups, pls very anxious to see your reply, tnx in advance

On May 8, 2015 at 7:11am
David wrote:

What is the input voltage of the UPS, I that’s is the more important of the ratings, and what about the connectors for the UPS? Are they the same with you battery that’s lying around?

On May 19, 2015 at 5:05am
Rekkha wrote:

hello Mr David,  sorry for the late reply .. The UPS input voltage is 240 V, AC. In India millions of ups sold for computer backup 10min backup time, just for shutting down the operating system, Regarding the connectors, this 7 Ah is insert type, not like the one in the car, but I can replace the connectors,  if there won’t be any damage to the ups unit, thanks David

On May 19, 2015 at 7:57am
David wrote:

Hi Rekha,
Of course the AC input of the UPS would be either 110 or 220/230/244V, but what is the required DC input of the UPS? If you do not exceed this input DC voltage, the UPS should be fine, but why use a UPS and not an Inverter? Inverter offers you flexibility of adding batteries based on time of use.

On June 3, 2015 at 8:06pm
Girish mahalingaiah wrote:

I am having a su-kam. Inverter 1400/24 pure sine wave,bought from my friend for my desktop computer for backup power.i just want to know what kind of battery I need to use for this inverter.I am having zero knowledge.
Thanking you

On June 5, 2015 at 1:53am
zetrohisoka wrote:

My fone’s battery is rated at 1300 mah. Wud it be ok to use a lower 750 mah as a replacement?

On June 5, 2015 at 3:40am
David wrote:

Hi Girish,
Make sure you do not buy lead acid battery if you are installing the inverter and battery indoor, your best buy is sealed deep cycle battery, you need 2pcs of such battery 2 x 12V = 24V and depending on how long you want to provide backup after power outage, you will decide on AH, 12V100AH will last twice as long as 12V50AH, so it all depends on your budget.

On June 7, 2015 at 7:58pm
Girish mahalingaiah wrote:

Thanks for the information

On July 6, 2015 at 7:04pm
Justin wrote:

I’m researching different power sources for a custom project and hypothetically speaking, can batteries be custom made to suit a custom purpose? I’m wondering in terms of size, shape, and desired power output… Looking at something with a large size allowance, would a battery that is 12” in diameter (disc shaped) be capable of harnessing a constant power output of 2,000 volts?? Just curious in its feasibility smile Thanks!

On July 10, 2015 at 11:16am
Susan wrote:

I have a 12v 35w battery for my alarm.  I can’t seem to get the same, could I use a 12v 45w or could that cause problems?

On July 25, 2015 at 12:10am
fidel wrote:

hi david, whats the truth about radiant energy charging like the one we see in a bedini pulse generator, have you tested or,tried one of these projects and seen the results?

On August 4, 2015 at 5:00am
Ruby Valdes wrote:

Hi, excuse me, I’m going to get a new battery but the only difference is that it says EB484659VA instead of EB484659VU is ther any diference?

On May 29, 2016 at 4:36am
Mulatu Biresaw wrote:

hi my name is Mulatu Biresaw students of automotive engine service in injbara polytechnic college.
1)please give me definition of automotive battery?
2)what is component of lead storage battery?
3)what is principal and construction of lead acid battery?
3)give definition of cell and battery arrangement?
please give me this question answer by email address

On September 28, 2016 at 5:04pm
Norman Fraser wrote:

What is the difference between a SLA Battery & Flooded Calcium ? Is it the medium ? (Water and caps on flooded calcium), cheers Norm

On November 8, 2016 at 2:13am
Mr kelly wrote:

Thanks alot!!.

On November 14, 2016 at 6:57am
Julie Hordon wrote:

Hi im hoping someone cane help me I have a child ride on car which has a battery of 6v 5ah i can not find a battery to match however could I use a 6v 7ah or 6v 7.5ah I would appreciate any help offered thank you

On November 23, 2016 at 8:01am
Diego wrote:

Hi. Need help. I have been looking info on it but I couldn´t find it

What does EN200 mean in a 12v 12Ah battery?


On January 4, 2017 at 8:01pm
Anjeet wrote:

We are using 3000mAH battery and applied load is 1.8Amp can you tell us what is the backup time for this.

On March 4, 2017 at 5:25am
Iliyan Nicolov wrote:

Hi, I’m looking to replace my motorcycle battery and I see definitions like TTZ10S on my old battery and LTZ10Son the new one’s. What is the difference between the letters and the number?
There are different numbers lower or higher. What the numbers mean?

On April 7, 2017 at 7:16pm
steve wood wrote:

Question, what does the “L” stand-for in battery ratings? Like, what does the “L” stand for in a L16 battery? Thank you

On April 23, 2017 at 12:39pm
Robert McCullough wrote:

difference on “AA” batteries among #4, #6, #8?

On June 10, 2017 at 6:24pm
Host4dummies wrote:

Is it correct to say 3000mAH is the same as 3AH due to the “m” meaning “milli” meaning 1000.

On June 30, 2017 at 11:33pm
noosh wrote:

how we can refer to your valuable notes?

On September 11, 2017 at 2:56pm
Godwin wrote:

I have 1.5kva inverter with 24v 200amp of battery but it’s no more lasting for 12hours,now I want to install 12v 600amp of battery using the same inverter.can it charge it comfortably and can it last like a week with about 300watts to 350watts load’s?

On January 2, 2018 at 11:36am
rakesh wrote:

hello sir we are into a project, its a battery operated device planning for long life on full charge, can you please suggest battery types to go with this project.

On January 12, 2018 at 9:09am
Jon Harding wrote:

I have a question for you about what is the meaning
for electrical definition for BRLIND this is from a
battery company in Germany Kreisler Electric they
have several conversion kits for electric vehicles.

I have a Aeronautical Engineering degree and because
of our prototype drones are all going to be electric
powered by using our PPU that will generate 20,000
contionuas volts we are looking for a storage unit or
a battery pack that is going to be the lightest one on
the market that will be able to make the drones fly for
24 hours with a 55 pounds of cargo into remote locations
so if you could answer my email
We are going to be needing a experienced Electrical
Engineer with 15 Years in the industry to bring onboard

Thanks for your help looking forward to getting your
message back.

Jon Harding

On March 12, 2018 at 9:28am
russell wrote:

i have a battery with connector labeled T D C . what do these stand for ?how to use them?

On March 5, 2019 at 11:53pm
Murat Tologlu wrote:

@Daniele UDEL could you find the answer of your question about “industry standard for the power rating of a battery” ? You can contact me at mtologlu@hotmail.com if you want to discuss.