Replacing bicycle light batteries is largely a matter of the brand and model of the light, as well as the type of batteries it uses. While some bicycle lights use standard AA batteries, others require NiMH or Li-ion rechargeable batteries, or pairs of disc batteries. Different bike lights also have widely different methods for removing the casing in order to get to the batteries to be replaced. Batteries for different bicycle lights do not all have the same replacement frequency. Some batteries may only last a few weeks or months, while recent technology has increased battery life of some types to a year or longer. Lastly, some bicycle lights must use an external battery pack to supply them with power. Assuming your bicycle light affixes to the handlebars and uses an internal battery, its replacement is not difficult.
Step 1: Remove Light from Bracket
Once you realize that the battery in your bicycle light is dead and either needs replacing or recharging, remove it from its mounting bracket. How this is done will depend on the light. Some have a button you press to release its lock, while others simply slide off a track.
Step 2: Open Light Casing
This procedure also depends on the construction of the bicycle light. While some bicycle lights have a cap attached to the main shaft of the light, others come with a casing that snaps into place over the internal mechanism and battery chamber. Those with caps usually have to be twisted from their locked state to open them up, sort of like an aspirin bottle. Depending on the quality of the light, they can be quite securely fastened. Bicycle light covers that snap into place will have a small opening at one end. Into this tab place a flathead screwdriver. You can also use a coin that is not too thick. Once in, use the leverage to pop the case in two. Whichever method your bicycle light uses, the batteries will then be visible and can be removed.
Step 3: Remove and Replace the Batteries
When you get the batteries out of their chamber, you can either replace them or recharge them. Some lights use NiMH or NiCAD batteries that are rechargeable. Newer lights may have Li-ion batteries that are also rechargeable. After enough recharges, though, even they will have to be replaced. When replacing, match the old battery with a new set just like it. If the light uses disc batteries, make sure the replacements are of the right size and voltage.
Step 4: Reassemble Bicycle Light
Once the batteries have been replaced and slid back into their chamber, either reattach the snap-together halves of the light casing or cap to the main shaft of the light. Turn the light on to make the batteries are in correctly and operational. Slide the light back onto its track on the mounting bracket.
Just like that, your bicycle light batteries have been replaced. Now that you know how to get inside of the light, replacement of the batteries in the future will be easy.