TL;DR: This small experiment shows how I used a smartphone to charge a camera battery. The method is not safe but It struck me as a great example to highlight the inaparrent compatibility between two seemingly unrelated devices.
Most current smartphones and other handheld tech devices operate on similar battery technology. Many incompatibilities are created deliberately by creating new battery shapes for every model. Although this creates safety by disallowing untested combinations of batteries and chargers, it also creates a huge market complexity. But hey, who has replaceable batteries in their phones today anyway?
Disclaimer: The method described in this post is very dangerous, particularly if you don’t know what you are doing. This is meant solely as an report on something that helped me get my camera charged without the proper charger at hand. The instructions given below are neither complete nor necessarily correct. Do not try this at home. (and if you still do you do so at your own risk).
My Canon 870 camera comes with a replaceable battery, which it cannot charge just by using the USB connection it connects to the computer with. Instead, the battery has to be taken out of the camera and charged with an external charging device.
So once in a while I find myself on a holiday with an empty camera battery but without that battery charger.
This time I thought – well my Samsung S4 Mini smartphone has a replaceable Lithium-Ion battery as well, and in fact it can be used – with the necessary caution – as a battery charger for Li-Ion batteries with similar specifications to the original phone battery. At a minimum the battery type, voltage, and temp sensing circuit should match, and the capacity of the photo battery should be lower or similar to the original battery capacity.
Warning: If you connect the wrong pins, or anything else goes wrong during this you are likely to harm your phone and/or yourself by e.g. setting the battery on fire. I supervised the whole charging process.
First I removed the original battery from the phone. The smartphone seems to have four connections to the battery: +, tempsense, -, and probably the NFC antenna. I then connected +, tempsense, and – to the photo battery. The 4th connector was left unconnected. Now I connected the USB charger adapter to the phone (and did not switch it on). The phone indicated it was charging. This way I managed to nicely charge the battery. In fact this slightly overcharged the battery, as the camera battery is 3.7V and the phone charger charges to 3.8V! . Ideally you would throw a fuse between the +/- connectors to make this more safe.
Basically, your phone has a fully functioning Li-Ion Battery charger. If you have a 3D printer, one would be easily able to build some nice charging adapters. Anyone up for a project?