3LR12 3R12 4.5 Volts Flat Battery
The alkaline 3LR12 battery is a flat, rectangular battery containing internally three "B" cells connected in series to form the 4.5 volts battery pack.
Once upon a time, the 3LR12 4.5V battery was a very common battery used in various applications, but nowadays, it is mostly used in flashlights, toy remote controllers, and similar applications.
Updated: October 7, 2022.
3LR12 Battery Features and Specifications
3LR12 battery feature physical dimensions of (H x L x W) 67 x 62 x 22 mm (~2.638 x 2.441 x 0.866 inches) - internally, it contains 3 (three) B-cell batteries (D x H: 21.5 x 60 mm) connected in series to provide the required 4.5 volts.
3LR12 4.5V battery is based on the Zinc-Manganese Dioxide (Zn-MnO2) chemistry, also known as "Alkaline" chemistry - nominal voltage is 4.5 volts, cutoff voltage is 2.7 volts, and nominal capacity in the 2000-3000 mAh range.
Note: nominal capacity depends on various factors, including temperature, battery age, drain current, etc. There are some sources that the 3LR12 battery features a capacity of up to 6000-8350 mAh, but that is hardly a realistic value.
Flat rectangular 4.5 volts batteries feature top battery terminals in the form of metallic strips, each 6-7 mm wide, with the positive battery terminal being shorter than the negative battery terminal.
The most common labels for 4.5V 67 x 62 x 22 mm flat rectangular battery are MN1203, 3LR12, 3R12, 1289, Type 3336, 4912 etc.
Zinc Carbon (3R12) vs. Alkaline (3LR12) 4.5V Battery
Zinc-carbon 4.5V battery is commonly labeled as a 3R12 battery and is used as a cheaper alternative to the alkaline 3LR12 battery, especially for low-drain devices.
On average, a zinc-carbon 3R12 battery weighs 105-115 grams and features a nominal capacity of 1000-1500 mAh, while an alkaline 3LR12 battery weighs 160-180 grams and features a nominal capacity of 2000-3000 mAh.
Also, the shelf life of zinc-carbon batteries is rarely longer than 2-3 years, while alkaline batteries can have a shelf life of up to 5-7 years.
Personally, due to the small, almost negligible price difference, alkaline 3LR12 batteries are highly recommended due to the more stable output voltage, higher capacity, longer shelf life, etc., for both low-drain and high-drain devices.
3LR12 batteries are being slowly phased out in favor of other battery sizes, for example, AA, C, and D. Also, the introduction of lithium rechargeable high-capacity cylindrical batteries and LED flashlights are making 3LR12 batteries slowly but steadily obsolete.
Photo: Varta flashlight from 70is or 80is, powered by 4.5V 3LR12 battery.
As one can see, 3LR12 and 3R12 4.5V batteries were quite popular for powering small incandescent light bulbs. And in combination with a simple mechanical switch, they were surprisingly reliable. The one in the photo still works :)
4.5V 3LR12 Battery Adapter
Since 4.5V flat batteries are not as popular as other battery sizes, for example, AA batteries, some brands offer 3xAA to 3LR12 battery adapters.
Such battery adapters allow the use of three AA batteries in an adapter that can fit the battery compartment intended for 3LR12 batteries.
And since AA batteries are available almost everywhere (local hardware stores, supermarkets, online shops, office supply stores, etc.), such battery adapters allow the users to replace a 3LR12 battery with three AA batteries.
Long Story Short: If You are looking for a flat 4.5V rectangular 67 x 62 x 22 mm battery, go for the 3LR12 battery from reputable brands - this is an alkaline battery, designed as a heavy-duty battery and already tested by countless real-life users...
But, if You need a low-drain battery for a device that will be used only occasionally, a 3R12 (zinc-carbon) battery can save You some money...