FESTO cordless drill CDD 12 battery holder

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This replacement LiPo battery holder can be used in place of FESTOOL BP12C or BPH12C batteries for FESTOOL CDD 12 ES or CDD 12 FX cordless drills. The holder includes a voltmeter to monitor the battery state and four magnetic bit holders. # History I've owned several cordless drills, but my favorite remains the FESTOOL CDD 12 due to its ergonomic design, which I've had for 17 years. Despite replacing the batteries multiple times, they don't last as long as the originals. When it was time to replace them again, I decided to switch to lithium. # Design Considerations The original NiCAD batteries have a nominal voltage of 12V, while LiPO cells are nominally 3.6V per cell and can reach up to 4.2V. This leaves you with the option of using either three or four LiPO batteries. I chose to use four, which provides a maximum of 16.8V and a nominal voltage of 14.4V. Although this is on the high side, it's likely that the engineer used at least 20V components, making it suitable. The simplest approach would be to remove the existing batteries and replace them with LiPOs, but I decided against it due to several reasons: - You need a spot welder to connect the cells together (soldering is not recommended). - A connector must be added for balanced charging. - Someone might mistakenly place the LiPOs in a NiCAD charger. - Replacing individual cells becomes more difficult. - You can use your standard LiPo charger. - The batteries can be shared between different devices. Instead, I opted for standard 18650 size that can fit into a 3D printed battery holder. # Battery Choice 18650 LiPO batteries are widely available. However, not all of them will work with a drill due to the high current requirements. For a drill, you need at least 15A peak and about 5A nominal. I chose the SAMSUNG INR18650-30Q's, which meet this requirement. Be cautious when purchasing 18650s, as many fakes won't deliver the necessary current. Update: May 2019 I was gifted a second drill of the same model (the batteries failed) and printed another battery holder in black. An alternative method for mounting the back battery contact is also shown, which involves attaching a flap contact with tape to the battery holder and two layers of foam tape for pressure. The contacts must be domed with a punch to ensure good contact.