The Doc uses a scientific
dooverlackie (the technical definition) that can put a load on a set of 4
batteries. A few observations about this test procedure:
- 10 ohms is used for all batteries
now. Some of the earlier tests on AA batteries used
a 5 ohms load.
(Alkaline batteries are not suitable for digital cameras as
the power is demanded faster than what an alkaline battery can
deliver. So while the battery may seem flat, in fact it is not. The
battery if left for a little while will recover and give further
- A set of four batteries is used.
The battery holder can be changed to allow for different size
- Data is normally logged at 5
seconds intervals (but that can be varied from 1 second up to 600
- Data that the scientific
dooverlackie can log includes: battery temperature, ambient air
temperate, humidity and voltage. Data is logged to a csv file for
analysis in a spreadsheet or graphing program.
- The test automatically cuts off at
3.6 volts. Batteries are generally considered flat at 0.9 volts. So 4
x .9 volts gives you 3.6 volts for a set of 4 batteries. The Doc has
found that rechargeable alkaline batteries can last longer and the Doc
drained them down to 3.5 volts without adverse consequences (but do
so at your own risk).
- Ni-MH and Ni-Cd are drained and
charged at least 10 times before being tested. As Ni-MH batteries, in
particular, do not take a full charge straight away. The charger used to charge a set
of batteries can affect battery performance. Some chargers are more
effective in charging battery types than others. The Vencon Battery
Analsyer is used as the benchmark charger.
- Each battery test has its own report,
in the form of 2 flash graphs.
The methodology is not perfect,
but it does give some idea of what to expect from different battery
brands. A different methodology will give a different result.
tests are basically comparisons of different battery types and
brands. But for any comparison you need a starting point. Since many
people do not own rechargeable batteries, they may find it difficult
to have a reference point for comparison. To establish a starting
point, the Doc tested carbon zinc and alkaline batteries.
the AAA size, the two primary cell alkaline batteries tested were the
Duracell Ultra and Everyready Gold. Here is a graph of the results:
load used on a set of 4 AAA batteries was 10 ohms. A fairly heavy
load for AAA batteries, but needed as this is the load used in
testing of the rechargeable batteries. In the real world this is a
worst case test. The batteries would last longer in most situations.
the AA size, the Doc also started with a set of K Mart carbon zinc
batteries (purchased for the princely sum of $1) and the Duracell
Ultra and Eveready Gold. Here is a graph of the results:
load used on a set of 4 AA batteries was 5 ohms, designed to reflect
the heavy drain on batteries by such devices as digital cameras. The
Doc was a little surprised at the durability of the two alkaline
batteries under such a heavy load. But we will see they cannot
compete against leading brand Ni-MH batteries, which can be recharged
over 500 times. The heavy drain of a 5 ohm load outstrips the ability
of carbon zinc and alkaline batteries to deliver the power. What this
means is that the battery will drop to 3.6 volts (the test cut off
voltage), but the battery will not actually be completely drained. If
left for several hours the battery will be able to used again. This
is also true of other battery chemistries, but it is more evident
with alkaline batteries. This graph clearly shows how an alkaline battery cannot
compete against a high capacity Ni-MH.
is important in two respects, first, ambient air temperature above
25 Celsius is not ideal during the charging process. Secondly, a good
charger should not overheat the batteries. The higher the heat during
charging and use, the shorter the overall battery life.
in Australia invariably means temperatures above 25 Celsius in
summer. In addition to using a charger that does not overheat
batteries, a simple but effective trick is to use a fan to help cool
the charger and batteries during charging. The Doc uses a cheap
desktop fan you can buy for a few dollars from the $2 shop. Warning:
Do not use this
type of fan for extended periods without a break, as the bearings are
often plastic and they will melt and may cause a fire.