The GLINK 21700-4000S lithium-ion (Li-Ion) battery has a capacity of 4000 mAh (4.0Ah), a voltage of 3.7V, and a power rating of 15Wh. It meets Thai Industrial Standards (TIS) and is rechargeable. It can be used with flashlights, power tools, DC electrical appliances, or assembled into battery packs by connecting them in parallel (to increase Ah) and in series (to increase V). It's suitable for a wide range of DIY projects.