Which Watch Battery do you need?
The interesting world of Watch Batteries!
All About Watch Batteries
We thought that you may find it useful for us to give you an insight into the interesting world of
watch batteries. (We know it's not that interesting, but it may help you order the correct battery!).
With respect to watch batteries there are 3 main types of chemistry, Silver Oxide, Alkaline or Lithium.
The Lithium button cells will be 3 Volt cells (apart from the Renata 751 which is a 2V lithium battery) and the Silver Oxide and
Alkaline button cells will be 1.5 Volt.
Therefore, the voltage of your application will dictate whether you will need a Lithium battery or not. The Lithium cells
tend to be the larger button cell batteries and their references tend to be prefixed with either CR or BR.
For example, a CR2032 is a Lithium battery.
Silver Oxide or Alkaline?
Since Silver Oxide and Alkaline watch batteries give the same voltage (1.5 Volts) then which battery do you choose?
Well, firstly Silver Oxide watch batteries tend to be more expensive than an Alkaline cell of the same size. So can you
just use the Alkaline watch battery of the correct size? Well, this depends on your application and if the Alkaline version is
available. There is a much wider choice of Silver Oxide watch battery sizes. In fact Rayovac make only two Alkaline button
cell sizes but approximately 30 different Silver Oxide watch battery sizes. Where Silver Oxide cells score over their Alkaline
counterpart is in their ability to maintain a more stable voltage. This characteristic makes them better for clocks and watches
and absolutlely essential for metering equipment (like light meters in cameras for example) where a stable voltage is
required. An Alkaline cell though is good for high current devices where a stable voltage is not required, for example,
in electronic toys and calculators. Many of those children's noisy books use LR44s (Alkaline), but can run
equally as well using the Silver Oxide equivalent (Rayovac 357). Many electronic toys use LR44s or LR41s and
there is no problem using a Silver Oxide watch battery of the equivalent size. Rayovac do not make a LR41 so we have no problem
in suggesting to owners of the Thunderbird Soundtech toys (which use 3 x LR41) that they can use the Silver Oxide
equivalent (Rayovac 392) instead. Since some of our customers have been charged £4.00 for each LR41 by High Street
jewellers, they have no problem in paying us for the more expensive Silver Oxide watch battery at a mere £1.50 each!
So to summarise, if your application calls for a stable voltage under load (watches, clocks, metering equipment etc.)
use a Silver Oxide watch battery. If not, and you can get the Alkaline equivalent then use that. And remember, you can
always use a Silver Oxide watch battery to replace an Alkaline watch battery.
Now this is interesting (honest). The Lithium button cell battery sizes are easy to determine from their reference numbers.
The first two digits refer to the diameter of the battery in mm and the second two digits give the height or thickness
of the battery in tenths of mm. So, for example, a CR2032 is a Lithium button cell which is 20mm in diameter and 3.2mm thick.
A CR2430 is a Lithium button cell which is 24mm in diameter and 3.0mm thick. There, told you that this was interesting!
Now having had this lesson, you will begin to see that other watch batteries also have a reference number
which give a similar clue to their size. Take for example a Vinnic L1154. Now you would be excused for thinking
that this was 11mm in diameter and 5.4mm thick. Close. But in this case the first two digits refer to the range
of the diameter and the second two again, as for the Lithium button cells, refers to the thickness in tenths of mms.
The diameter in this case is in the 11mm range. A quick check in our reference table
will show that all watch battery diameters in the 11mm range are 11.6 mm in diameter. Therefore, a L1154 is an
Alkaline button cell 11.6mm in diameter and 5.4mm thick.
Other manufacturers use a similar reference numbering system for their watch batteries, and as a general rule
wherever you see a three or four digit reference number for a watch battery it is likely to follow the rule described above.
For example, a Sony SR626SW is a Silver oxide watch battery which has a diameter in the 6mm range and is 2.6mm thick.
All watch batteries in the 6mm range have a diameter of 6.8mm. So a SR626SW is 6.8mm in diameter and 2.6mm thick giving
a Rayovac equivalent battery, from the reference table, as a 377.
Other manufacturers, like Rayovac, number their batteries without giving a clue as to the size of the watch battery,
so to refer from these to other manufacturers' batteries you really need to use a
cross reference table
What do the letters at the beginning of the reference number mean?
So what about these prefixes? This is just down to experience I suppose
so here's a short list. Manufacturers who use SR to denote a Silver Oxide watch battery will tend to use
LR to denote Alkaline. Those which use SG to denote Silver Oxide will tend to use AG to denote Alkaline.
- BR/CR = Lithium
- L = Alkaline
- SR = Silver Oxide
- LR = Alkaline
- SG = Silver Oxide
- AG = Alkaline
The letters at the end of the reference number are different, one is W the other SW. Which one do you choose?
In the Silver Oxide range of batteries you will often see a different suffix to the same battery reference. For example
you can get a SR1130W and a SR1130SW. The ¨SW¨ refers to use in low drain devices whereas the ¨W¨
refers to high drain devices. So what's the difference? Well you would tend to only use a ¨SW¨ battery
in a watch without a backlight. Your standard analogue quartz watch would be fine with a low drain watch battery, whereas
a watch which used a backlight would really need a high drain ¨W¨ watch battery. Having said that, you could
quite happily run a low drain watch using a high drain watch battery. ¨SW¨ batteries will tend to have a slightly
longer life when used in low drain devices than their ¨W¨ equivalent. If in doubt use the high drain ¨W¨
type since there is likely to be little or no difference in price.
Battery Capacity and Shelf Life:
Just a few words on battery capacity. This tends to be given by the manufacturers in mAh (milli Amp hours)
and this figure gives us an idea how much current can be supplied by the battery and for how long. For example, a battery
which had a capacity given as 40mAh will be able to supply 40 milliamps for an hour or 20 milliamps for two hours. We can
provide this information if you like, but you don't need to know this if you are replacing a watch battery in household
gizmos. Really it's for the electronic buffs who need to know which battery to use in a newly designed circuit.
The shelf life of watch batteries is determined by storage temperature and their chemistry. Typically, at 21 degrees
Celcius a Silver Oxide battery will lose less than 10% a year, an Alkaline button cell about the same and Lithium button
cells less than 2% a year. This loss decreases as the storage temperature decreases.
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