BU-303: Confusion with Voltages

A battery is an electrochemical device that produces a voltage potential when placing different metals in acid solutions. The open circuit voltage (OCV) attained varies according to the metals and acid solutions (electrolyte) used. Applying a charge or discharge places the battery in the closed circuit voltage (CCV) condition; charging raises the voltage and discharging lowers it. This voltage behavior is governed by the internal battery resistance; a low resistance produces less fluctuation under load or charge than a high one. Charging and discharging agitates the battery and a full stabilization takes up to 24 hours. Temperature also has a role; cold rises the voltage and heat lowers it.

Manufacturers rate a battery by assigning a nominal voltage and with a few exceptions, these voltages follow an agreed convention. Rating some Li-ion higher than the standard 3.6V/cell may help in product marketing but for the user, a chemistry-specific voltage counts. 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 (OCV), the voltage of a fully charged battery should be 2.10V/cell. Keeping lead acid below 2.10V/cell will cause the buildup of sulfation.

Nickel-based

In consumer applications, NiCd and NiMH are rated at 1.2V/cell, industrial, aviation and military batteries adhere to the original 1.25V. There is no difference between the 1.2V and 1.25V cell; the marking is simply preference.

Lithium-ion

The nominal voltage of lithium-ion had been 3.60V/cell. This is a practical figure because it represents three nickel-based batteries connected in series (3 x 1.2V = 3.6V). Some cell manufacturers mark their Li-ion products as 3.70V/cell or higher. This poses a marketing advantage because of higher watt-hours on paper (multiplying voltage times current equals W). It also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series. Let this higher voltage not cause confusion; equipment manufacturers will always adhere to the nominal cell voltage of 3.60V for most Li-ion systems, and the standard designation of 10.8V and 14.4V will always work.

How did this higher voltage creep in? To calculate the nominal voltage, we take a fully charged battery that measures 4.20V and then fully discharge it to 3.00V at a rate of 0.5C while plotting the average voltage. For Li-cobalt, the average voltage comes to 3.6V/cell. Performing the same discharge on a fully charged Li-manganese with a lower internal resistance will result in a higher average voltage. Pure spinel has one of the lowest internal resistances, and the plotted voltage on a load moves up to between 3.70 and 3.80V/cell. This higher midpoint voltage does not change the full-charge and end-of-discharge voltage threshold.

The phosphate-based lithium-ion deviates from others in the Li-ion family and the nominal cell voltages are specified at between 3.20 and 3.30V. Because of the voltage difference, the two lithium-ion families are not interchangeable. New lithium-based batteries will have other voltages and specialty chargers may be needed.

Primary Batteries

The alkaline delivers 1.5V, silver-oxide 1.6V and primary lithium 3V. The 9-volt battery has six cells in series. Do not charge primary batteries because overcharge can produce explosive gases. See Reusable Alkaline

Comments

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\
benelmokadem
harry potter movies in order

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

I wonder how many more projects are out there secretly