LR521, SR521, 379, AG0 button cell batteries are often used in wrist watches, toys, remotes, and similar low drain devices.
These batteries are manufactured by most, if not all, most reputable battery brands and are easy to find if you know what to look for.
Updated: December 29, 2021.
SR521SW/379 Batteries Features and Specifications
SR521SW/379 button cell batteries feature physical dimensions of (D x H) 5.8 x 2.1 mm (0.2283 x 0.0827 inches).
Like most similar button cell batteries, SR521SW, 379, LR521, SR521, AG0 batteries feature two main chemistries - alkaline and silver oxide.
LR521 Battery Equivalent
Alkaline 5.8 x 2.1 mm batteries are commonly labeled as LR512, LR63, AG0, 379 and similar - they are recognizable thanks to the 'LR' or 'AG' prefixes, although some manufacturers use numbers only labels, but also describe the battery chemistry on the package of the battery.
The nominal voltage of LR63/LR512/AG0 batteries is 1.5 volts, but as the battery is used, voltage drops. Cut-off voltage depends on the device used, but generally, it is around 0.9-1.0 volts.
The typical capacity of alkaline 379 battery is around 10 mAh, also depending on the common temperature, drain current, battery age, and similar.
Some of the most popular LR521 battery models on the market include (Amazon links, the links open in the new windows):
SR521SW Battery Equivalent
Silver-oxide 5.8 x 2.1 mm batteries are commonly labeled as SR521, SR521, SR521SW, SR63, 379, SG0, and similar.
These batteries differ from alkaline batteries by mostly having the prefix 'SR', although some brands use 'numbers only' labels and similar. In order to attract potential customers, most of the brands write down the labels of the models that their batteries actually replace.
Of course, this sometimes increases the confusion about which battery to buy, but generally greatly simplifies finding proper battery replacement.
The nominal voltage of SR521SW/379 batteries is 1.55 volts and the typical capacity is in the 15-18 mAh range, which is significantly more than the alkaline typical capacity of 10 mAh.
The cut-off voltage of silver-oxide batteries is ~1.2 volts, but this also depends on the cut-off voltage of the device in use.
In any case, silver-oxide batteries have much more stable voltage than alkaline batteries, they have a larger capacity and longer shelf life.
Some of the most popular SR521SW battery models on the market include (Amazon links, the links open in the new windows):
SR521SW/379 Batteries Comparison Chart
The following chart lists some of the most popular SR521/379 batteries with their most important features and specifications:
| Battery Datasheet | Chemistry Nominal and Cutoff Voltages | Capacity Discharge Current | Operating Temperature Annual Self-Discharge Rate |
| Duracell D379 | Silver Oxide 1.55V, 1.2V | 16 mAh, 68kΩ @20°C down to 1.2V 22 μA | 0°C to +60°C ≤10% @20°C |
| Energizer 379 | Silver Oxide 1.55V, 1.2V | 18 mAh, 68kΩ @21°C down to 1.2V 22 μA, @1.52V @21°C over 68kΩ | - ≤3% @20°C |
| Renata SR521SW | Silver Oxide 1.55V, 1.2V | 16 mAh, 47kΩ @20°C down to 1.2V 32.6 μA, over 47kΩ @20°C | -10°C to +60°C ≤5% @20°C |
| Varta SR521SW | Silver Oxide 1.55V, 1.2V | 15 mAh, 68kΩ @20°C down to 1.2V - | 0°C to +60°C - |
As one can see, the most popular button/coin 5.8x2.1 mm cells are silver-oxide batteries featuring a nominal voltage of 1.55V and cutoff voltage of 1.2V.
However, actual capacity depends on the temperature, battery age, and discharge conditions, but on average, it is in the 15-18 mAh range.
SR521SW/379 Batteries Safety Issues
SR521SW/379 batteries are small and shiny objects that can attract pets and kids that may swallow them - that is the reason why the SR521SW/379 and similar batteries are delivered in pets' and kids' safety packages.
Although modern button/coin cell batteries don't contain toxic mercury, cadmium, and similar pollutant, and although SR521SW/379 batteries feature low voltage and relatively low capacity, if they get swallowed, they can cause chemical burns due to the electrolytic reactions in the body.
Again, SR521SW/379 batteries feature small voltage and relatively small capacity, but ...
If something like that happens, contact the nearest emergency center, explain to them what happened, and follow their instructions.
Note: when dead batteries are swallowed, they can cause mechanical injuries as well ...
SR521SW/379 Batteries Frequently Asked Questions (FAQ)
Here are some of the most common Frequently Asked Questions about SR521SW/379 batteries and button/coin cell batteries in general:
What are 379 batteries used for?
SR521SW/379 batteries are used in wrist watches, calculators, medical equipment (thermometers, glucose meters, and similar), remote control fobs, micro LED flashlights, some laser pointers, and similar.
What battery replaces SR521SW?
Any button/coin cell battery with physical dimensions of 5.8 x 2.1 mm and a nominal voltage of 1.5-1.55V can replace the SR521SW battery.
However, that battery should be preferably a silver-oxide battery due to the better voltage stability, larger capacity, and longer shelf life than similar alkaline batteries.
Such batteries are labeled as SR521, SR521, SR521SW, SR63, 379, D379, SG0, etc.
Is 377 battery the same as 379?
No, 379 battery feature physical dimensions of 5.8 x 2.1 mm and 377 battery feature physical dimensions of 6.8 x 2.6 mm.
What is the smallest size watch battery?
There are several very small watch batteries with SR416SW/337 battery featuring physical dimensions of only 4.8 x 1.6 mm (0.18897 x 0.62992 inches).
Are button batteries toxic?
Generally, no, they are not toxic, however, if they get swallowed they can cause chemical burns and mechanical injuries.
Long Story Short: if you need a button cell battery 5.8 mm in diameter and 2.1 mm in height and you are not sure which one to get, follow these rules:
- LR521, LR63, AG0 and similar are alkaline batteries: cheaper, but also less stable voltage and lower capacity,
- SR521, SR521S, SR521SW, SR63, 379, SG0 and similar are silver-oxide batteries: they cost slightly more, but have more stable voltage and higher capacity. Also, their shelf life is longer.
If you have wrist watch or any similar electronic device, be sure to get a battery that is labeled SR521SW and/or 379. Personally, the price difference between alkaline and silver oxide batteries is very low and performances of silver-oxide batteries, IMHO, justify buying silver-oxide batteries.
