External Li-ion Battery for Digital Cameras

An external battery is useful for taking extra photos and videos as they have a higher capacity than the LiPo batteries that come with your camera. They can also replace difficult-to-find batteries in your backup cameras, which you may sometimes use for your projects. Because they are cheaper on a watt-hour basis, you can bring several cells on a long trip. You can even take apart a laptop battery for a free Li-ion cell. I'll be using my 2MP Canon S330 model as a working camera.

• Voltage: 3.7V
• Battery size: 18650 rechargeable Li-ion
• Capacity: ~2500 mAh (versus 1000 mAh)
• Options for using NiMH AA batteries
• Also suitable for cellphones

Materials

• Wooden block
• Digital camera
• 18650 li-ion battery (e.g. used laptop batteries, Deal Extreme)
• 18650 li-ion battery holder
• Camera battery (used to match the size)
• Two-pin connectors
• Heat shrink tubing
• Quick setting epoxy
• Small copper sheet

Tools

• Multimeter (to ensure correct polarity)
• Dremel
• Sanding and grinding pieces
• Saw (circular saw preferred)
• Quick setting epoxy
• Soldering iron
• Hot melt glue gun

Mark the battery's dimensions on the wood and saw it. The block can be cut a bit wider or longer since you're going to sand it anyway.

Warning: When using power tools, always wear eye-protection.

Use a coarse grinding disc to trim the wood until it fits the battery compartment. Use sandpaper to smooth the surfaces.

Drill a hole to lead the wires out of the plastic flap of the battery compartment.

Mark the "+" and "-" contacts on the wood. The battery pack may state the polarity, but if it doesn't, you can test it with your multimeter.

Note: The T (thermistor) terminal was left out for my camera. For some models, it will work fine, but others may require you to sacrifice a used battery pack with the circuit board inside. You'll have to take out the LiPo battery and wire the 18650 holder to the circuit board so that the polarity matches.

Make grooves for the wires and contacts by grinding it.

Cut them the size of the original battery contacts.

Thread wires through the hole first. Tin the metal strips before soldering them to the connectors with the correct polarity.

Glue the contacts with epoxy and use a clamp to hold them in place until they set. Make sure you line them up properly.

This step is important. Before installing it, test the polarity with a multimeter so that it matches that of the original battery pack. Reverse polarity can damage your camera. Always make sure that you insert the battery correctly into the holder. To make it easier to identify the polarity, you can add a blob of solder onto the positive terminal.

With a 18650 cell, you can now take more than twice as many photos on a single charge. To increase the capacity further, simply install them in parallel. Multi-cell 18650 holder can be modified for parallel configurations. Two cells in parallel would double the capacity and make it useful if your camera will be on all day. This might look like overkill but since aged batteries have a higher internal resistance and reduced capacity, it may work.

Other chemistries like 3 NiMH AA cells will also work. They have a similar capacity and voltage.