Some exotic cells in sizes of 14500 (AA), D and specialized 3.7 to 12v LiPO packs are cheap and easy to obtain but the battery CHARGERS are often difficult to find or VERY expensive. These types of packs and bundled cells are also VERY sensitive to charging rates, temp and current! OR they Explode.
PCB's and special chargers can be had or built from scratch. However free or cheap voltage converters available off the shelf, workbench power supplies are DANGEROUS!
This instruction will show rechargeable battery types, several sizes with codes and nomenclature along with their compatibility with conventional sizes.
Use these in Lights, small toys & Appliances and RC planes and Cars.