|The second worst thing about
digital cameras, after their price, is their battery consumption. Even
models without power-sucking LCD screens and flashes still eat batteries
faster than film cameras, because of the amp-hungry onboard electronics.
Many digital cameras run from AA cells (a "battery" is more than one cell),
usually four of them, and they’re renowned for draining a set of alkaline
cells in less than an hour of shooting. Sometimes much
My own Kodak DC120 can certainly do this trick. Its
current draw varies from 200mA (milliamps; 1000 milliamps are one amp) when
it’s turned on but not doing anything to about 1.2A when its LCD screen is
in full power-vampire mode. It can peak at about 2A right after taking a
If you look at the specifications for AA cells,
though, you’ll find that an ordinary AA alkaline is meant to have a capacity
of 2.4Ah (amp hours). This means it should be able to deliver 1.2A for two
hours before going flat. But it falls far short of this performance. Why?
Cell capacities are commonly quoted based on a "C/20"
load – a load that flattens the cell in 20 hours. A 2.4Ah AA cell can be
asked to deliver more than ten times C/20 by a camera. In this situation,
its voltage drops precipitously and its life is greatly reduced; the most
demanding cameras draw so much current that they can’t run from alkalines at
D size alkalines have a capacity of around 15Ah. This
makes them rather good value, when you consider that they cost only about
50% more than AAs. The C/20 load for a 15Ah cell is 750mA, so they’re only
facing about twice their rated load from the average digital camera. D cells
will therefore deliver rather more of their rated capacity into such a load
than AAs. But you still won’t get the duration you’d expect.
Newer kinds of alkalines like Energizer’s "Advanced
Formula" and Duracell’s "Ultra" cells perform a bit better under high-load
conditions, but not a lot. Lithium AA cells cost three times as much as
alkalines and can in medium-draw applications like film cameras give three
times the life – although two times is a better bet – but, again, they don’t
much like the super-high loads from digital cameras and will give you poor
value for money. "Rechargeable alkaline" cells are worse yet. Don’t even
think about using cheap dry cells.
A cell that can’t deliver high enough current to run a
camera any more will probably have a fair bit of capacity left for
less demanding applications. So if you’re using alkalines in your
digital camera, don’t throw them away when the camera says they’re
flat – try them in a lower current device, like a pocket radio or a
remote control. You may be surprised how long they last.
Rechargeable cells have capacities much lower than
those for alkaline non rechargeable ("primary") cells. About 1Ah is a common
rating for good nickel-cadmium (NiCd) and nickel metal hydride (NiMH)
rechargeables. Cheap NiCds often have a capacity of only 600mAh; NiMH AA
cells are available with capacities up to 1.3Ah. These cells also have a
lower output voltage – only 1.2 volts against the 1.5 from non-rechargeables.
But they handle high output currents much better than
the primary cells, because their internal resistance is more than ten times
smaller. Under a 1A load, 1.5 volt alkaline cells of all sizes commonly
droop to only 1.1 volts. But a 1.2 volt NiCd’s output voltage will barely
droop at all, and it’ll deliver its full rated capacity without breaking a
NiCd and NiMH cells have a lousy "shelf life" – the
length of time they’ll hold a charge, just sitting there. About half of
a NiCd’s charge will leak away in a month, and NiMH cells are even
worse. So if you leave your camera sitting around with rechargeables in
it, bear in mind that surprisingly little charge may be left when you
suddenly need to use it.
For this reason, and because they’re much cheaper in
the long run, rechargeable cells are very popular among digital camera
users. Two or three sets of rechargeables should last for an afternoon of
photography, if you go easy on the LCD and flash usage. On the down side,
ordinary NiCd chargers take at least a few hours to pump these cells back up
again. "Trickle" chargers take about 14 hours.
The solution to the long charge times problem is a
better charger. For this, forget the electronics store, and go to a hobby
shop. You can get a charger intended for model car battery packs for around
$100, and many such chargers are eminently capable of charging a digital
camera’s cells – all you need to do is buy a 4xAA cell holder for less than
$2 and put a connector on it that the charger can plug into or clip onto.
And hobby chargers reliably detect the slight voltage drop that signifies
end-of-charge, and support charge currents up to five amps or more.
Not that this is necessarily a good idea. Charge a set
of ordinary AA NiCds at 5A and they’ll probably be too hot to hold at the
end of the charge, and may "vent" – ooze electrolyte. High charge currents
don’t charge these cells much faster – most of the excess energy is
dissipated as heat. For these ordinary low performance NiCds, a charge
current of 500mA is plenty, and some hobby chargers do not support this low
a charge current. Why? Glad you asked.
While you’re at the hobby shop, check out the
batteries that the hobby chargers are designed for. Model car packs are
built out of special high current C-size cells, the best of which are made
by Sanyo. These cells, with capacities of 1.4 or 1.7Ah, can handle repeated
20A discharges with peaks of 40A or more, and endure charge currents of five
amps and higher. The super discharge capability isn’t necessary for digital
camera applications, but the superfast charging can be handy. At 5A, a 1.7Ah
pack can go from flat to full in less than half an hour (you have to put
about 1.4 times the capacity of a cell into it to charge it). There are 2Ah
cells as well, but they’re more expensive and not quite as tolerant of harsh
treatment. All of these cells are NiCd; for a long time, no rechargeable
battery technology even approached NiCd’s high current performance.
Nowadays, though, you can get sub-C NiMH cells with
3Ah capacity. They're the same size as NiCd sub-Cs, but weigh less, and can
tolerate quite rough charging and discharging. There are lots of lower
current NiMH cells with capacity well beyond that of NiCds as well; you have
to be more careful charging them (they can't be charged as fast, and a
charger that says it's only for NiCds is only for NiCds...),
but they're a very sensible option for home-made packs.
The preceding paragraphs were my way of introducing
you to my preferred solution to the camera battery problem – the big fat
outboard battery pack. The simplest such pack is a D cell holder with
alkaline cells in it. You can get a four D cell holder from any electronics
store for a few dollars. The one in the illustration cost $AU2.30 from
Jaycar. To connect the holder to the camera, you’ll need a lead that can
plug into your digital camera’s AC adaptor connector. If your camera does
not have such a connector – some very cheap ones don’t -
you’ll need to hack something onto the battery connections, or just get a
The connectors used by digital camera AC adaptors are,
almost without exception, simple two-terminal "barrel" plugs. The easiest
way to get a suitable lead is to cut one off an AC adaptor, but if that
doesn’t appeal, you’ll be pleased to know that electronics stores stock
barrel plugs in all sizes. There are several commonly seen sizes, and the
5.5mm outside diameter ones which are most popular have two possible inside
diameters, so take the camera and/or an AC adaptor with you and get it
right. A connector with too large an inside diameter can result in
annoyingly intermittent power.
Making up your own cable also allows you to use
stouter wire than is used in most plugpack leads. Pretty much any hook-up
wire is thick enough to comfortably carry the current drawn by a digital
camera, but thin wire is fragile, and a battery pack lead will get twisted,
trodden on, pinched in zippers and who knows what else. A good compromise
between robustness, manageability and price is medium duty figure-eight
speaker cable, or "zip cord", so called because you can "unzip" the two
insulated wires from each other by pulling them apart. Check out the
offerings at your local electronics store; it should cost you well under a
dollar a metre.
It helps to have a nice long cable from the pack to
the camera, so you can leave the "anchor" sitting on the floor and be able
to pace about a bit. For field photography, I keep the battery in my
backpack along with the other camera paraphernalia. Smaller batteries fit
easily enough into a "bumbag" ("fanny pack", to Americans; in some other
parts of the world, this sounds vaguely rude), but this can be rather
uncomfortable with larger ones. You’d think having a power plug sticking out
of your camera all of the time would be very cumbersome, but with the DC120
at least I’ve found my monster battery pack to interfere surprisingly little
Building a big battery
Putting it all together is a simple soldering job. If
you’ve never soldered, this is a great time to learn; an iron, a stand and a
big reel of solder will set you back less than $40 (Australian dollars -
even less in US currency). If you don’t want to learn, your local
electronics technician will be able to do it for you in minutes if asked
(and/or paid) nicely.
Make sure you get the polarity of the connector right.
Most barrel plugs are wired "tip positive"; the outer, "sleeve" terminal of
the plug is the negative. If you’re uncertain, use a cheapo multimeter to
check the output from the plugpack. You can now buy digital multimeters
quite good enough for basic tasks like this for less than $20 from various
Even D size alkalines, though, aren’t particularly
efficient when driving digital camera loads. NiCds are much better. Really,
really BIG NiCds are better yet.
(Note: When I first wrote this piece,
NiMH cells weren't yet a good option for this sort of application. Nowadays
good NiMH cells are easy to get, and so are hobby chargers that understand
them. If I were building this same pack today, I'd use D-sized NiMH cells.
Bear that in mind as you read the NiCd-plugging below.)
The pack I use with my DC120 is made out of NiCds so
large that most people don’t even know they exist. They’re Sanyo F size
cells, one size up from D, with a capacity of 7Ah. There is only one larger
standard size, M, with a 10Ah capacity. I got my F cells from the USA; in
Australia you can expect to pay something like $30 each for them. The much
more common 4.4Ah D cells sell for about $15 each, and are a rather more
sensible proposition. M cells, in case you’re interested, cost the thick end
of $70. Each.
I’ve GOT a mains adaptor for my DC120, but thanks to
the 7Ah pack I practically never use it. I plugged it in for the first time
in months in order to get the pictures of my battery pack cabling! Doing
things like serial data transfer and LCD screen image reviewing under
battery power is a terrible idea if you’re using AA cells, but with the
monster pack – no problem. I have never run the big pack flat.
Nor, by the way, do I intend to in order to "maintain
the pack’s capacity", because I do not subscribe to the myth of "memory
effect". If you think your camera, laptop, cellular phone or cordless drill
battery suffers from memory effect, you are wrong.
Eagle-eyed readers will note that my pack contains not
four but five cells. The five cell pack gives the camera 6V, with which its
motorised zoom works noticeably faster than when it’s running from the 4.8V
it gets from four NiCds.
Like many electronic devices, the DC120 works from a
range of voltages. It will run just fine from four NiCds, but it’s happier
with a higher voltage – its mains adaptor is rated at 8V. A NiCd pack that
delivers less than the rated voltage of a camera’s mains adaptor should
cause no problems; mains adaptors do not deliver less than their rated
voltage unless they’re delivering more than their rated current, which you
shouldn’t force them to do. When delivering less than their rated current,
most plugpacks deliver MORE than their rated voltage. Only "regulated"
plugpacks maintain the same voltage at all times.
To build a custom battery pack, you’ll need to solder
the cells together. Soldering to cells can be tricky – you need a soldering
iron with a fairly large tip, and you need to roughen up the ends of the
cell a little with sandpaper or a file to encourage the solder to stick –
but you can get around the problem by using "tagged" cells, which cost maybe
25 cents more each and have a solder tag sticking out from each end. The
tags are very easy to solder to, and can handle currents much higher than a
digital camera will ever draw. Do not attempt to solder any kind of cell
straight to another cell – use wire in between.
If you MUST solder to untagged cells – and you may
have to if you want to use really high capacity NiCds for your camera –
practice on a few non-rechargeable cells first. Roughen the ends, apply the
iron and some solder to "tin" them, then press the wire you intend to use
into the solder blob with the iron. If you roughen the ends properly and
have a decent iron, it should all be over in five seconds. If you find
yourself heating the end of the cell for ages, you’re doing it wrong.
Some resellers of NiCd cells, like for example E. H.
Yost & Co, offer solder tags as an option on their entire range. The cells
don't come from the factory that way, but the resellers weld them on
themselves. Done correctly, this is every bit as good as a factory-installed
Once you’ve got your tagged cells or learned to solder
to untagged ones, arrange your cells as you like, and stick ‘em together.
Hot melt glue is a decent adhesive for battery pack assembly – it holds
quite firmly, but not TOO firmly, and gives you some time to get the line-up
right. The cells should be aligned so it’s easy to wire the positive of each
cell to the negative of the next, with the power cable attached to the
terminals on the ends of the line. What exact arrangement you use depends on
what size cells you’re using and how you intend to carry the pack; shuffle
the cells around until you’re happy.
You can, if you like, use a sealed lead acid (SLA)
"gel cell", as used for standby power in alarm systems, to power your
digital camera. Gel cells come in 12V and 6V versions; the 6V batteries will
power many digital cameras just fine. I prefer NiCds, though, because lead
acid batteries are rather heavier for a given capacity, can’t be charged
nearly as fast as a NiCd, and don’t like being run flat. If you flatten a
gel cell and don’t charge it fairly promptly, it will die. For this reason,
always make sure any gel cell you buy is charged – another use for that
If you use alkaline cells in a holder, you only need
to solder your cable to the holder. If you go for a rechargeable pack, the
battery lead will need a plug and socket arrangement in it somewhere that
you can unplug, so you can connect the battery pack to a charger. You could
also wire a barrel socket matching the plug to the charger if you liked. My
own battery pack has a couple of Anderson connectors with specifications
many times higher than are needed for this application. Anything that won’t
come unplugged when you don’t want it to will do, but remember the golden
rule of all connectors – if there’s a male and a female, the FEMALE
connector is the one that should be on the "live" cable that comes out of
the battery pack. Otherwise, unplugging the connector will leave a live male
connector dangling around, and male connectors are so called because they
have protruding terminals, which can easily short out on any metal object.
Short circuits are especially bad with NiCd and NiMH cells, because their
low internal resistance lets them deliver enormous currents when shorted,
and they can and do start fires.
Incidentally, because of the huge current capacity of
NiCd cells, it's not a bad idea to put an in-line fuse in the power
lead from any NiCd packs you build. If you don't, and the lead shorts
out, the cells will probably still not be damaged - but the lead can
easily get red hot, then melt. This is probably not exactly what you
want to happen in your camera bag.
A 5 amp slow-blow
fuse should give plenty of headroom for even power-hungry digicams,
but will blow long before your cable overheats.
If you’ve never charged your NiCd or NiMH cells, they
should be flat; that’s the way they come, and that’s the way they should
stay while you’re building a pack out of them. These kinds of cells, unlike
lead acid batteries, are perfectly happy to stay flat for as long as you
like, and putting the pack together while the cells are flat removes the
danger of short circuit excitement.
Once you’ve built the pack, give it a bit of a charge,
check its voltage with your multimeter, and if all is well plug it in and
see if it works. Once you’ve verified that it does, mummify it. I wrap large
packs with several layers of cloth-backed "Gaffa" tape ("duct tape", to
Americans; actually, the Gaffa brand stuff is inferior; Nashua 357 tape is
the real gaffers’ choice). You can also get heat-shrink tubing in
surprisingly large sizes (again, ask at the hobby shop!), but it’s hard to
beat cloth-backed tape for durability and price.
What about lead acid?
On the face of it, Sealed Lead Acid (SLA) batteries of
the type used for alarm system battery backup and in computer
Uninterruptible Power Supplies (UPSes), to name just a couple of their many
applications, look like a good alternative to NiCd. They use much the same
basic reaction as a lead-acid car battery, but their jellied electrolyte
(they're also referred to as "gel cells") means you can use them in any
orientation without suddenly finding yourself covered with sulfuric acid,
and they need no maintenance.
Five 4Ah 1.2 volt NiCd cells will cost you more than
$70 (Australian dollars) retail with no charger, whereas a 6 volt, 4Ah SLA
battery is only $20, plus $30 for an "intelligent" plug-pack charger that'll
switch to a gentle trickle mode when the battery's full. It looks like a
no-brain decision, doesn't it?
Well, it isn't. The problems with SLA batteries are as
- They're darned heavy. SLA weighs roughly twice as
much as NiCd for the same capacity. They take up about the same amount of
space, but if you're on the road, or just wandering around a party, you'll
be acutely aware that the word "lead" in their title is not just there for
- They've got a smooth discharge curve. NiCds keep
their voltage almost steady for almost all of their discharge, whereas
SLAs fade away more rapidly, so in some applications you can't use the
last 10% or 20% of the battery's capacity because the device being powered
thinks its battery is flat. This is not normally a problem with digital
cameras, because they're made to work with alkalines, which droop severely
under a 1A load even when new.
- SLAs don't like going flat. If you run a lead acid
battery flat and leave it for several hours, it'll sulfate and you might
as well throw it away. Even the deep-cycle traction batteries don't like
being flat for too long. SLAs definitely can't be left
- Slow charging. 10 hours is about as fast as you can
charge a SLA. You can charge even plain, non-fast-charge NiCds in 90
minutes with a good charger; fast charge NiCds can be charged in less than
If you've already got a pile of camera gear, throwing
a couple more kilos of battery in there won't make too much
difference, I suppose. But most digital camera users don't have a lot of
accessories (because they can't have a lot of accessories -
there just aren't that many available for most digital cameras!) and it's a
pain to tote around a super-heavy battery.
But they're cheap, all right. If you mostly stay in
one place, or you don't mind lugging a really dense battery pack around, SLA
could fit the bill. All good electronics stores stock them, so when you go
shopping for battery options, pick one up and see how you feel about it.
Personally, I and my underdeveloped musculature are sticking with NiCd.