BU-303: Confusion with Voltages

Explore why some battery packs pose odd voltages and how this affects the user.

A battery is an electrochemical device that produces a voltage potential when placing metals of different affinities into an acid solutions (electrolyte). The open circuit voltage (OCV) that develops as part of an electrochemical reaction varies according to the metals and electrolyte used.

Applying a charge or discharge places the battery into the closed circuit voltage (CCV) condition. Charging raises the voltage and discharging lowers it. The voltage behavior under a load and charge is governed by the current flow and the internal battery resistance. A low resistance produces low fluctuation under load or charge; a high resistance causes the voltage to swing excessively. Charging and discharging agitates the battery and full voltage stabilization takes up to 24 hours. Temperature also plays a role; a cold temperature lowers the voltage and heat raises it.

Manufacturers rate a battery by assigning a nominal voltage, and with a few exceptions these voltages follow an agreed convention. Here are the nominal voltages of the most common batteries in brief.

Lead Acid

The nominal voltage of lead acid is 2.00 volts per cell, however when measuring the open circuit voltage; the voltage of a charged battery should be 2.10V/cell. Keeping lead acid much below 2.10V/cell will cause the buildup of sulfation. While on float charge lead acid measures about 2.25V/cell; higher during normal charge.


In consumer applications, NiCd and NiMH are rated at 1.20V/cell, industrial, aviation and military batteries adhere to the original 1.25V. There is no difference between the 1.20V and 1.25V cell; the marking is simply preference.


The nominal voltage of lithium-ion is 3.60V/cell. Some cell manufacturers mark their Li-ion as 3.70V/cell or higher. This offers a marketing advantage because the higher voltage boosts the watt-hours on paper (voltage multiplied by current equals watts). The 3.70V/cell rating also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series rather than the more familiar 10.80V and 14.40V respectively. Equipment manufacturers adhere to the nominal cell voltage of 3.60V for most Li-ion systems.

How did this higher voltage creep in? The cell manufacturer plots the voltage of a fully charged cell that measures 4.20V, discharges it at 0.5C to 3.00V and takes the mid-way point. For Li-cobalt the mid-way point is about 3.60V. The same scan done on Li-manganese with a lower internal resistance gives an average voltage of about 3.70V. It should be noted that the higher voltage is arbitrary and does not affect the operation of the portable devices or the setting of the charger.

The phosphate-based lithium-ion has a nominal cell voltage of 3.20V and 3.30V; lithium-titanate is 2.40V. This voltage difference makes these chemistries incompatible with regular Li-ion in terms of cell count and charging algorithm.

Primary Batteries

Alkaline delivers 1.5V, silver-oxide 1.60V, zinc-air 1.40V and primary lithium 3.00V to 3.90V, depending on system. Mercury-based batteries have been withdrawn for environmental reasons. The 9-volt battery has six alkaline cells in series.

It is not recommended to charge alkaline batteries because overcharge can produce explosive gases.. (See BU-211: Alternate Battery Systems – Reusable Alkaline) Do not attempt to charge primary lithium batteries as this may lead to an explosion.

Last Updated 2015-09-16

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On March 3, 2011 at 5:06pm
BWMichael wrote:

its funny how people think a lithium battery with 3.7v written on the packaging is better than one that says 3.6v

On March 7, 2011 at 7:03am
Edward Baxter wrote:

I am in Mexico. Can I use a 3.6v lithium as a replacement for a 3v lithium in my dive computer.

On March 18, 2011 at 3:05am
MAHESH wrote:

want details of batteries

On May 14, 2011 at 5:34am
dean mancis wrote:

hi just wondering what is the current flow in a singel 12v headlamp circuit with 100w globe is it 10A?  And how much current will flow through a cicuit that has a 12volt power supply and a resistance of 6 ohms is it 2 Amps .  What is required to drive 1.5A of current through a 30 ohm load is it 45v?

On May 25, 2011 at 5:56am
Robert Atkinson, Jr. wrote:

The author made a slight error in the formula for energy. Volts (V) times Amps (A) equals Power in Watts (W), not energy (Wh). Since power is energy per unit of time, then Power (W) x time (hours) equals energy (Wh). To convert Watt-hours to Joules (the MKS measurement system’s preferred unit) Multiply Watt-hours by 3600 sec/hour to get Joules (1W= 1Joule/sec, and 3600 sec=1 hour, or 60 sec/minute x 60 minutes/hour= 3600 sec/hour).

On August 25, 2011 at 12:19pm
Ian wrote:

What voltage is required to charge a 12 volt gel battery . IAN

On December 3, 2011 at 9:09pm
Man Man wrote:

“Italso” - sounds like an Italian battery company. Needs a space, as does “series.Let”.

On December 3, 2011 at 9:10pm
Man Man wrote:

And “(OCV)attained”.

On September 19, 2012 at 2:23am
mark wik wrote:

love your site. hopefully i will learn many things and impress my friennds and associates with my knowledge of battery and charging technology. thanks, mrw

On January 22, 2013 at 3:13am
shaibu wrote:

how to calculate the total heat loss of VRLA batteries.

On August 26, 2013 at 7:22am
omar wrote:

Can i charge my li-ion battery with a 9v ac adapter?

On November 26, 2013 at 3:29am
Ajay Pundir wrote:

just love your site. it has increased my knowledge of batteries and charging technology. thanks

On January 20, 2014 at 4:42am
jeeva wrote:

Sent me email for battery information

On February 27, 2014 at 4:04am
harry potter wrote:

do you use skype? If yes we can also discuss there. -  It would be awsome if a discussion of e.g. batteries could be done between different scientist via skype or something else, so that everyone get soon help…
i just want to ask something about that battery and explain me how to make it in russia\
harry potter movies in order

On April 20, 2014 at 9:52am
ruby wrote:

I wonder how many more projects are out there secretly

On October 6, 2014 at 7:01am
sandeep wrote:

Sir is there any problem in charging a 1.2 volt battery by a 9 volt dc. 2000 mA output charger

On December 2, 2014 at 1:57am
Zeinab wrote:

hello people , actually i am inquiring about OCV most problem and how it affects the battery

On December 3, 2014 at 3:51am
SHAILENDRA jain wrote:

can we connect in a battery bank of 12 v 150ah battery with 12 v 100ah battery .

On January 6, 2015 at 6:40am

My car is alto k10 maruthi, pls inform me using horn details,battery volts and horn volts.

On February 7, 2015 at 9:54pm
Iain wrote:

I removed a 3 volt CR2 lithium battery from my security system because I had a low battery reading. I am puzzled because after removing it, I found that the battery still read 3 volts. Can you explain this?

On February 17, 2015 at 12:47am
Tevita Kirailevu wrote:

When reading an analogue meter , which place in it should i read the battery voltage (can you send a image of it on where to locate it.

On February 18, 2015 at 10:03am
tony wrote:

i am not satishfy with the seriese combination of cells.

On March 18, 2015 at 3:59pm
James Traxel wrote:

My instrument rechargeable battery got weak and I went to replace it.  It is an “A” size battery.  When I measured the voltage it was 1.8 v.  How can this be?  The battery that I purchased was NiMH of 1.2 v so I’m left scratching my head.

On March 22, 2015 at 6:46pm
JM wrote:

If you still have the curiosity itch, try measuring the battery voltage under load (while it’s being used by a device). This should give you an accurate reading as to how much voltage your battery is really pushing. Do this at your own risk and be careful. Plan how you’re going to go about measuring it (don’t allow the positive and negative to touch each other and you’ll be fine). Probably not worth the risk, but the idea is there if you want to try it.

On March 24, 2015 at 1:16am
krishna wrote:

How much highest ratting of dc batteries

On April 22, 2015 at 9:16am
Tom wrote:

I am currently charging a battery (inside a device, and I have no details about it, I just know it is rechargeable).
Using my universal power supply, I have the voltage up and the current reduced to 200mA. Currently the voltage is at 8.87V. any ideas what voltage will indicate a full charge?

On August 31, 2015 at 6:36pm
Bishwo wrote:


I have a 6V battery to run my system which also works in 6 volt that draws 0.5 AH. I made a parallel combination with two 12AH to make 24 AH so that I don’t need to recharge the battery for 48 hours. Once accidentally connected negative to positive and positive to negative which damaged the system and I had to repair it. DO you think that accident has any impact on the battery? Can I use the same battery again to run the system?

On September 24, 2015 at 11:35pm
HardwareFreak wrote:


How to calculate the time taken for a Li-ion battery to discharge from 4.2V to 3.4V, @ 2A load current…?
Can anyone pl help.

On October 2, 2015 at 7:54am
enver salimov wrote:

i thing this is so beatufull

On November 5, 2015 at 8:52am
JEC wrote:

Typical battery charger puts in Amps not volts correct?
As dc amps goes in, doesn’t battery voltage increase?