3.7V Lithium Polymer Batteries — 501–⁠1,999mAh

Within 501–1,999mAh, more capacity almost always means a larger cell, so the useful question is how much runtime you actually need before the enclosure has to grow. These are selection directions, not fixed device categories:

• 600–900mAh — a compact runtime upgrade over the ≤500mAh class, still easy to fit in a small device.
• 1,000–1,200mAh — an approximate 1Ah reference point for moderate runtime in a still-compact pack.
• 1,500–1,800mAh — more runtime while staying in compact-portable territory, before moving up to the high-capacity class.

Confirm the finished-pack dimensions (cell plus PCM, tabs, insulation, wires and connector) against your cavity, and validate continuous and peak current for your real load. If no standard model matches your space or runtime, a custom LiPo battery can be built to the required dimensions.