ALKALINE BATTERIES FOR CYCLE LIGHTS COMPARED
by Francis Cooke
A slightly adapted reprint
of the article first published in
Arrivee, November 1999
The Test
Initial Voltage under load
(CatEye bulb, 4.8V 2.4W
Time taken to drop to 4.8V
(for 4 cells in series)
Time taken to drop to
4.0V
Time taken to
drop to 3.0V
The Best
in Test
The Worst in
Test
Table of
Results
Addendum (2004/2006 - new formula alkalines, and high-capacity NiMHs)
As I mentioned in the previous issue, I've recently run a group test on various
brands and types of alkaline battery.
(Pedantic note: in this article I frequently refer to 'battery' when I should more correctly say 'cell' - a single AA cell is a 'cell' and not a 'battery' - 4xAA cells is a 'battery' - I use the terms interchangeably for the sake of readability, and not because I don't know the difference!)
There are several 'new formula' alkalines on the market - for example
Duracell Ultra (blue flash on the packaging) and Energizer Advanced Formula
(yellow flash on the packaging). They cost more, and in some cases this is not
optional - Tesco's for instance are only offering 'Extra Long Life' in packaging
which is typical of the new breed "New longer lasting" "50% more power in high
drain applications eg Mini Disk Player, Krypton Torch". Sony's packaging claims
100% improvement. Duracell's website shows a set of curves suggesting a
performance boost of 30% or more for their 'Ultra' batteries.
So it's tempting to assume that these new types may offer longer
life in our cycle lights.
My test was very simple - just fit a set of 4 AAs to a CatEye Micro and
measure runtime to total extinction. The same Micro with the same bulb was used
for each test, in a reasonably constant ambient temperature of around 15°C. The
test was repeated and averages taken in an attempt to reduce sample variation.
Although crude and open to criticism, this test has the merit of being
relevant to a real-world application for these cells - running a CatEye Micro
during a long night ride.
Just for interest, as well as a dozen varieties of alkaline cells I also
tested a set of Energizer Lithium AAs. NB these are NOT rechargeable cells (eg Li-ion) but primaries, just like the alkalines on test here.
I judged the performance of the batteries in four ways:
Initial
Voltage Under Load (CatEye bulb, 4.8V 2.4W)
Time taken to drop to 4.8V (for
4 cells in series)
Time taken to drop to 4V
Time taken to drop to 3V
(This is effectively 'runtime')
Initial Voltage Under Load
Typically the cells dropped from an
open-circuit of around 6.35V (for 4) to around 5.75 under load. So right from
the word go, this so-called 6V light is under-performing.
The best were the
Energizer Advanced Formula, which dropped to 5.9V. This equates to a
brighter, whiter light when you first switch it on.
Close behind were
Varta Maxi-Tech, on 5.86V.
The poorest performers were the
Varta 'blue & white' cells which immediately dropped to 5.42V, and the
standard Duracell and Energizer types also did badly.
Time taken to drop to 4.8V.
This is the point where the CatEye Micro
drops to an 'undervolt' condition, moving from efficient, white light towards inefficient, yellowing light. I think this is the most under-estimated aspect - in the real-world bike lighting situation, this is a very important measure. The
sad truth is, that typically this took just 30 minutes - with most alkaline
cells and a Micro, you get half-an-hour of good light, and its all downhill from
there.
Easily the best cells by this measure were the Boots Extra Long
Life - 47 minutes.
Sainsbury Extra Long Life and Panasonic Photo were
next best with 33 minutes - but that's a long way back.
Varta 'blue/white'
only managed 12 minutes, Duracell 20 and Energizer 25.
The Energizer Lithiums were superb in this part of the test
- 3 hours 10 minutescompared with just 47 minutes for the best alkalines - if
you like the CatEye Micro and you like bright light, you really have to consider
using these expensive cells.
Time taken to drop to 4.0V.
I judged that at this voltage the light
was still 'useful' - not great, but not bad either. So this is perhaps the best
way to compare these cells. Typically they took around 2h30 to drop to this
voltage.
The same three brands did best - Boots Extra Long Life 3
hours 07 minutes, Sainsbury ELL and Panasonic Photo the only
others to reach 3 hours.
Varta 'blue/white' managed just 2 hours,
and Duracell, Duracell Ultra and Energizer were not a lot better - 2h15.
(NB - for the NiMH cells that have been added to this test at a later date, this 4V point should be seen as the absolute max run time. The best cells can go well over 4h to this point.)
Time taken to drop to 3.0V.
I judged that at this voltage the light
was still 'usable' - poor, and getting close to total extinction, but definitely
still a usable light in dark conditions. Randonneurs will want to know about
this figure. Typically it took around 3h20, by which time the light was dimming
rapidly with total extinction occurring 10-15 minutes later.
Best in test by
quite a big margin, was Energizer Advanced Formula - 4 hours 10 minutes.
Next came Varta Maxi-Tech, 3h52, and then Boots ELL, 3h40.
Varta
'blue/white' managed only 2h25, Duracell Ultra 2h40, Duracell 2h45.
I
couldn't believe how badly the expensive Duracell Ultras had done throughout
this test, so I ran another set down to see if it was a freak result. It wasn't.
The Energizer Lithiums only managed 4h35 - not much more than the
same manufacturer's alkalines and a very disappointing result.
(NB - matched, or nearly so, by some high-capacity NiMHs added to the test later.)
Best Buys:
Clearly for runtime the Energizer Advanced Formula
stand out as the best in test. Usefully, they are very commonly available in the
UK, in all sizes. With multibuy deals you can get the price down to £3 for 4
AAs. Be sure to get the packs with the yellow flash on, because the Energizer
'standard' which did not do well in this test, are still available in very
similar packs but without the yellow flash - in fact the cells themselves look
identical.
Boots Extra Long Life I would say are equally good - they
fall short in total runtime but for 3 hours they are brighter than the
Energizers - and are readily available at a slightly lower price point, again in
all sizes. They are also, by a whisker, the lightest alkaline cells tested, and
interestingly they do not make any claim to be 'new formula'.
Varta Maxi-Tech and Sainsbury Extra Long Life get honorable mentions -
while Panasonic Photo are obtainable very cheaply from some sources and at £1.35
for 4 or even less they give easily the best bang-for-buck.
Avoid:
The Vartas that did so poorly had a sell-by of less
than 2 years. But they were incredibly cheap - £3.99 for 20 from Dixons. Good
for commuters, perhaps - though NiCad would be better. I am inclined to think
that the short sell-by was a major factor here, and I think the real message
here is - avoid any alkalines with less than 3 years on the sell-by date!
Duracell and Energizer 'standard' formulations, and Tesco ELL, were below
average and to be avoided, Sony Endura and Kodak Extralife were OK but nothing
special.
What to say about the remarkably bad results from the Duracell
Ultras? These could cost you £4.99 for 4, and yet only the dismal Vartas
saved them from being worst in test.
They did give a very bright light for
the first hour or so, almost as bright as the Lithiums. This suggests a low
internal resistance and more current flow, which in turn may account for the
pathetic run time, 1h30 short of the best. In other words (Duracell might argue)
I was not measuring the total capacity of these batteries, in which terms the
Ultras might do better.
The fact remains that, in our real-world cycle
lighting application, they simply did not deliver. My suggestion is: don’t use
them.
Initial V Time to 4.8V Time to 4V Time to 3V
Energizer A.F. 5.90 0h32 2h46 4h10
Boots E.L.L. 5.82 0h47 3h07 3h40
Sainsbury E.L.L. 5.80 0h33 3h03 3h30
Varta Maxi-Tech 5.86 0h31 2h44 3h52
Panasonic Photo 5.76 0h33 3h00 3h22
Sony Endura 5.75 0h29 2h40 3h27
Tesco E.L.L. 5.75 0h25 2h27 3h07
Kodak ExtraLife 5.74 0h27 2h25 3h40
Energizer 5.62 0h25 2h16 3h10
Duracell 5.52 0h20 2h15 2h45
Duracell Ultra 5.82 0h32 2h15 2h40
Varta 5.42 0h12 2h00 2h25
Energizer Lithium 6.24 3h10 4h10 4h35
Addendum (2004) -
new formula alkalines, and high-capacity NiMH comparison:
These figures are not exactly comparable with the table above, since although the test procedure was similar, it didn't use the exact same bulb, and also the ambient temperature was probably a bit higher (global warming ... ;-)
Alkalines have been marketed with 'new formula' continually since 1999 when this test was done - here are some very new cells for mid-2004 ...
Initial V Time to 4.8V Time to 4V Time to 3V
Energizer Ultimate 5.75 0h37 3h05 4h05
Good results, as good as the Best in Test, but not really much better than the Energizer Advanced Formula, 1999 vintage, that they replace.
High-capacity NiMH AA cells have improved steadily since this test was done and cells labelled as high as 2700mAh are now (2006) available. They are rechargable, and fairly lightweight - so an attractive proposition. In theory, these could be an alternative to some of the options listed above, and in the long run far more economical of course.
Vanson NiMH 2300mAh 5.00 1h05 2h20 2h28
HFE NiMH 2500mAh 5.36 2h00 3h55 4h03
7DayShop 2700mAh 5.38 2h45 4h23 4h37
These really show a discharge profile that is difficult to compare directly to alkalines - simply, they are very different, have different strengths and weaknesses. In the mid-range - 5V down to 4V - they compare very well indeed.
Some notes about NiMHs:
1. Capacity - actual usable capacity is most unlikely to be as high as the marking on the cell. However it does seem true enough that a higher-marked cell will generally be better than a lower-marked one (provided your charger can handle it).
Partly this discrepancy is marketing hype, partly its due to the 'normal' conditions of charging and use not being the same as the 'ideal' conditions under which the cells would be measured. Fast smart charging is the best method for general use, but it does not get the maximum charge into the cells - for this you need an ultra-slow trickle charge, which most domestic chargers are unable to provide, and which would in any case be intolerably tedious for most users.
2. The initial voltage (for 4 cells) for these rechargables is well below that for all types and brands of primary cell - the voltages above were taken after a period of at least 12 hours 'rest' after coming off charge, the actual voltage under load immediately after charging was quite a bit higher, but this isn't a real-world scenario for cyclists.
So the initial brightness of the light is a quite a bit down on any of the alkaline cells listed - but actually this disadvantage only lasts for 30 minutes or so, after that the NiMHs come out on top, for quite a long time.
3. The 4V point (for 4 cells) should really be taken as the 'runtime' for these rechargables - to be kind to your batteries and get good cycle life (number of recharges) you really should not run them down past this point - unlike alkalines which can of course be flogged to death. In other words, when the light starts to go from yellow to brown - switch it off - don't run it right down. In any case, with NiMHs, you will only lose 10 or 15 minutes runtime at most.
Even so, its worth noting that the best of these cells has a runtime (to 4V per 4 cells) which challenges the superb Lithiums (to 3V per 4 cells ie exhaustion).
4. The time to 4.8V is excellent - much better than even the best alkalines.
So good brightness is maintained for much longer, using these rechargables.
5. The times to 4V and 3V show a very rapid drop-off between these points, and so in usable brightness - in other words these cells die rather suddenly and without much warning. Many modern lights and other devices (eg GPS) are a 'aware' of this and have a shut-down feature to save the batteries from deep discharge - this can shorten the effective runtime (but will definitely lengthen battery cycle life).
Basically the voltage curve is much flatter, with a decent level of brightness maintained for longer before a sudden (and premature) drop-off. This makes these cells very suitable and economic too, for commutes and short night rides, giving bright light for all that time - but completely unsuitable for all-night rides using the Cateye Micro as in this test. (Modern 1W led lights are another matter of course - the best NiMHs are easily capable of running a 1W led all night, with a light output comparable to the Cateye Micro - this 1999 test is a bit dated in that respect.)
6. Charging - to maintain cells like this in good condition, it is essential to use a good 'smart' charger - otherwise capacity will soon deteriorate. Smart charging ensures good cycle life and reasonable performance. Slow charging (more than 5 hours) and timer-controlled charging are not such good methods, and will result in shorter cycle life. Arguably this is not that important, with newer better cells still coming to market on a regular basis, batteries tend to get replaced prematurely anyway. Ultra-slow trickle charging (and I'm talking about 2 days here) may get the best performance out of your cells, but is not the best method for long cycle life.
This graph highlights the strengths of good NiMH batteries (green lines) and Energizer Lithiums (red line) against a few alkalines including the best 3 in test, running in a Cateye Micro.
Back to Alkaline Batteries
Page
Back to Bicycle
Lighting Resource Page