Can i use two CR123 batteries instead of an 18650 Battery?

CR123 (sometimes known as CR123A) and RCR123 (a lithium-ion rechargeable version with higher nominal voltage) cells are very common in photography and torch use. They account for the largest amount of end user replacement cell sales in the photography industry, being used in both the camera and flash equipment. They’re also sometimes known as 16340 batteries.

So can you use two CR123 batteries instead of an 18650 Battery? Does one 18650 equal two CR123A?

Lets examine the differences in order to get the answer (or skip straight to the bottom for the quick version!).

Size – An 18650 battery is 18mm wide and 65mm long. A CR123, CR123A or RCR123 (a rechargeable variant of the normal CR123 like our Eagtac version) is 16=17mm wide and 35mm long. Putting two of these together leaves you 1-2mm short in width which isn’t a huge problem, but it also puts you at almost 5mm longer and this can be a problem. A device designed to use two CR123 cells will allow for this. A device designed to take an 18650 might not. Forcing the cap onto a torch designed for an 18650 for example may crush the positive button tops on a CR123, or crush internal components leading to a short circuit and potentially a fire/explosion. Likewise, a device designed to take two CR123/RCR123 batteries might accept an 18650 in physical size, but the output of the device may be poor (in the case of torches/flashlights) or may not work at all if it requires more than 4.5V to operate.

Capacity – Typical capacities for CR123/RCR123 cells range from 700mAh to around 1500mAh per cell/battery although they’re normally around the 1000mAh mark. 18650 batteries are available anywhere up to 3500mAh per cell/battery. If your device is designed to take an 18650 battery, you’re actually doing yourself a disservice using CR123/RCR123 cells instead, by having less available capacity. Putting two 1500mAh CR123/RCR123 cells into a torch/other device doesn’t give you 3000mAh because you’re putting them in in series, i.e., positive to negative. You can only increase capacity with parallel connection.

Voltage – Touched on briefly above but we’ll open it up here – Series Vs Parallel connection. Connecting batteries in series increases voltage, adding them together. The nominal voltage of an 18650 battery is in almost all cases, 3.6V. A non-rechargeable lithium CR123a is 3.0v and an RCR123 (rechargeable lithium-ion) is 3.6V. Using two CR123/RCR123 in series (one stacked on top of the other) therefore increases the voltage to 6v and 7.2v respectively. Your product might not be designed for this. Likewise, a device designed to take two CR123/RCR123 batteries might not work correctly at the lower voltage supplied by a single 18650.

So there you have it. The answer is ambiguous in some cases and clear cut in others but the simplest answer is, check the manual/instructions for the product and use the manufacturer recommended size because they specify  a battery or combination of batteries for a reason and that reason might not always be immediately obvious until it’s too late!

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