Battery Data

Which batteries are best?

I have always been baffled by the choices in batteries. Which brand will make my device run the longest? Which is the best value? I want answers.

I have begun testing commonly available batteries.

The process:
  1. Purchase battery.
  2. Monitor the voltage of the battery as it discharges into a 14.5 Ohm resistance - the load.
  3. Calculate the total charge delivered (Amp-hours or Coulombs) and energy delivered (Joules).
  4. Publish the results here.
  5. Repeat for next battery.
Summary of test results.
Company, model Size Type Amp-hours Joules
Energizer Ultimate Lithium AAA Lithium 1.28 6476 a
Kodak Xtralife AAA Alkaline 1.18 4840
Ace (Hardware) 3016607 AAA Alkaline 1.13 4840
Energizer Max AAA Alkaline 1.08 4660
Rayovac High Energy AAA Alkaline 1.08 4460
Duracell (MN2400) AAA Alkaline 0.97 4320 b
Evergreen Alkaline AAA Alkaline 0.97 4080
Energizer Industrial AAA Alkaline 0.94 4055
Duracell Optimum AAA Alkaline 0.84 3900
Rayovac Alkaline AAA Alkaline c
Rayovac for Low-Drain AAA Carbon-Zinc 0.34 1430 d
AAA Alkaline

When comparing batteries, pay attention to the energy content, the Joules. For most electronics, this number determines how long the battery will power the device.

(a) The Energizer Ultimate Lithium battery stands out for its stable voltage. Most batteries drop in voltage as they discharge but the lithium battery stayed over 1.3 volts for 90% of its life. See lab notebook 3.
(b) Duracell's packaging doesn't show a name for this battery. On their web site it is called "Coppertop" and MN2400. If you look closely at the battery, the MN2400 designation is there. The packaging claims a 10 year shelf-life and the batteries have a "MAR 2030" mark.
(c) I'm pulling the Rayovac Alkaline result because I can't retest it as local stores are no longer selling it. It was one of the first batteries I tested and at that time my system calibration was probably not accurate. See the notebook page for more info. (The Rayovac web site says that they were recently bought by Energizer. Could it be that this battery is discontinued? That would make sense as it performed poorly in my tests.)
(d) Although the energy in this battery is low it has the advantage of being safer for electronics. Alkaline batteries leak after a few years and seriously damage whatever the chemicals touch. Carbon-zinc batteries are "dry" and won't leak.

Energy, power definitions
The joule is a unit of energy.
The watt is a unit of power. Power is the rate at which power is delivered or used. The watt is defined to be a rate of one joule per second.

Turning that around, a joule is one watt-second.
Energy = power x time
One watt-hour equals 3600 joules. (That makes sense, since there are 3600 seconds in an hour.)
One kilowatt-hour equals 1000 watt-hours or 3600000 Joules.

Current, charge definitions
The coulomb is a unit of electric charge. (One coulomb contains 6240000000000000000 electrons!)
The ampere, or amp is a unit of electric current. Current is the rate at which charge is delivered or used. The amp is defined to be a rate of one coulomb per second.

Turning that around, a coulomb is one amp-second.
Charge = current x time
One amp-hour equals 3600 coulombs. (I think you see a pattern here!)
Rechargeable batteries are often rated in milliamp-hours or mAh. One milliamp-hour equals 0.001 amp-hours.

The connection between Energy, Voltage and Charge
Voltage, expressed in volts tells you how much energy is in each coulomb.
So if a battery delivers 100 coulombs at 1.5 volts, it has delivered 150 joules of energy.
Energy = charge x voltage

J = joules
W = watts
Wh = watt-hours (1 Wh = 3600 J)
kWh = kilowatt-hours (1 kWh = 1000 Wh)
C = coulombs
A = amps
mA = milliamps (1 mA = 0.001 A)
Ah = amp-hours (1 Ah = 3600 C)
mAh = milliamp-hours
V = volts

Battery life web pages

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