LiPo

A lithium polymer battery, or LiPo, is a rechargeable electrochemical cell that uses lithium metal oxides as the cathode material and houses the electrolyte in a polymer gel rather than a liquid. The polymer electrolyte is typically polyvinylidene fluoride (PVDF) mixed with lithium salts, which allows the battery to function safely at room temperature while being much lighter and more flexible in form factor than traditional lithium-ion cells with liquid electrolytes.

The defining advantage of LiPo batteries in industrial and trade applications is their high energy density relative to weight, typically delivering 100 to 150 watt-hours per kilogram. They come in varied form factors: pouches (soft rectangular packs), prisms (harder rectangular casings), and cylindrical cells. This flexibility means LiPo batteries are the standard power source in cordless power tools, drones, portable lighting, and battery packs for construction sites where weight and bulk matter. A typical 18V LiPo pack for a drill might weigh 1.5 to 2 kilograms while delivering 2 to 5 ampere-hours of capacity.

LiPo batteries require careful handling because the polymer electrolyte is flammable and the cells are sensitive to physical damage. Puncture, crushing, or exposure to temperatures above 80°C can cause thermal runaway: a cascade of internal chemical reactions that generates heat and can ignite the electrolyte. For this reason, LiPo packs include protection circuits that disconnect the battery if cell voltage drops below 2.5V (indicating deep discharge) or exceeds 4.2V per cell. On job sites, damaged LiPo batteries must be stored in metal containers or fire-rated cabinets away from other materials, not thrown into ordinary waste.

LiPo cells are typically wired in series (to increase voltage) and parallel (to increase capacity). An 18V pack contains five cells in series, delivering nominally 18 volts when fully charged (actually 21V at full charge, 15V at complete discharge). A pack labelled 18V 5Ah means five cells in series and enough parallel branches to store five ampere-hours total. Balancing circuits inside the pack monitor each cell independently to prevent one cell from overcharging while others lag behind.

The term lithium polymer distinguishes this chemistry from earlier lithium-ion batteries that used liquid electrolytes in cylindrical or prismatic housings. LiPos emerged in the late 1990s and rapidly became dominant in portable power tools because they tolerate deeper discharge cycles, recover better from partial discharge states, and can be shaped into thin pouches. However, they cost slightly more per watt-hour than equivalent lithium-ion cells and have a shorter calendar lifespan if stored fully charged, so total cost of ownership across multiple years may favour liquid-electrolyte alternatives in stationary applications.

In the trade, LiPo refers specifically to the cell chemistry and construction method, distinct from "18V battery pack" or "cordless drill battery", which are the finished assemblies. A single LiPo cell is rarely encountered loose on site; instead, LiPo packs come pre-assembled with connectors (XT60, Dean's T-connectors, or proprietary tool connectors) and integrated or clip-on management electronics. Understanding whether a site stock uses LiPo or older nickel-cadmium packs matters for charging infrastructure, storage safety, and disposal protocols.