mints was chosen as the enclosure, by the virtue of primarily its size
(the battery perfectly fits with enough spare space for board and electronics), material (elastic polyolefin,
resistant to breaking), and availability.
Digital cameras eat a lot of power. Even with a spare battery, one can not make more than few hundreds of shots. There are power banks with over ten amp-hours on sale, but the cameras typically do not support external power supply.
Stock chargers for the batteries usually come as mains-powered, require to be plugged into a wall.
It is easier to carry a USB-grade power source in one's pocket than a wall socket with mains power.
The stock chargers are also much bulkier, require a mains cable, and their proprietariness makes them liable to be lost or misplaced.
Two cameras need to be covered. One (Canon) uses NB-11L battery, the other (Sony) uses NP-FG1 or NP-BG1 type. The batteries have the same width, almost the same length, but different thickness and different position of contacts. Electrically they differ only slightly in capacity (2.2 vs 3.4 Wh), otherwise they are identical. Of course there Can Not Be some standard for Li-ion batteries.
An empty box of Tic Tac mints was chosen as the enclosure, by the virtue of primarily its size
(the battery perfectly fits with enough spare space for board and electronics), material (elastic polyolefin,
resistant to breaking), and availability.
The paper label was peeled away, the remaining adhesive was covered with a layer of butter, left
soak for about a half hour, then wiped away with a paper towel.
 TicTac box |  TicTac box |  TicTac box |  TicTac box |
 TicTac box |  butter used for glue remains removal |
An off-the-shelf miniature circuitboard module with TP4056 charger chip was chosen on the basis of availability.
The same module was also used for a Powershot A2600 internal charger
.
The board had a mini-USB connector, unsuitable for the task. The board was also a bit too long. The connector part was therefore cut away with a Dremel cutting wheel.
A custom-made breakout board for a microUSB connector was used. The 1.5mm circuitboard was ground to lower thickness (under half millimeter) to facilitate soldering to the substrate.
 Charger board |  Charger board, cut |  Charger board, cut |  Battery and charger board mockup |
 Battery and charger board mockup |
The electronics and the battery contacts are mounted on a piece of single-sided copper-clad board. The board was cut to size with a Dremel wheel. Copper sheetmetal U and L shapes were cut, bent and soldered to hold the battery in place.
Electrical contacts for the battery were chosen to be taken from connectors. The connector contacts are made from highly conductive highly springy copper alloy. The contacts were bent to shape and soldered to the proper positions on the base board.
Two sets of contacts were used; pairs for the wider-contact NP-FG1, and single ones for the narrow-contact NB-11L. Of course the batteries have incompatible contact pad layout, how else dear capitalism, so despite near size compatibility they had to be positioned on the opposite sides of the board.
The charger board was attached to the base board using a piece of doublesided foam tape.
The microUSB connector breakout board was attached by soldering at several points to both the ground plane and a small cutout for the 5V power. The cutout was wired to the charger board power input.
 Base board |  Base board |  Base board |  Base board |
 Base board |  Base board with electronics |  Base board with electronics |  Base board with electronics |
 Base board with battery in place |  Base board with battery in place |  Base board with battery in place |  Base board with battery in place |
 detail of contacts |
Replacement of the battery is done by removing the base board from the box. To facilitate this, a finger cutout was made by a hot knife in the bottom side of the box.
A small cutout was made in the box top in order to facilitate direct visibility of the charger LEDs.
A cutout for the microUSB connector was made in the living-hinged lid in order to facilitate direct accessibility of the connector. Original plan to have the connector hidden under the lid was decided against based on the limited life of the hinge and higher mechanical loads on it when attached to the charger and carried in pocket in open state.
 All in box |  All in box |  Finger-pushout cutout |  Finger-pushout cutout |
 Finger-pushout cutout |  Board in box |  Board in box |  Board in box |
 Viewport for lights |  connector port |
The resulting unit is a rugged, compact pocket-sized battery charger, capable of running from any USB power bank or any smartphone charger. The larger battery fits perfectly. The smaller battery, with contacts on the opposite side, is rather finicky to attach; the connector pins need to be bent a little occassionally; this is however a secondary issue as that one camera was modded for in-camera charging.