Portable Water Purifier Battery: A Custom Lithium-Ion Pack for Pumps, Valves and Control Systems

A portable water purification system does not place a simple, constant load on its battery. Pumps can draw a high current at startup, solenoid valves require stable voltage, and a cooling module may create short power peaks. At the same time, the complete battery pack must fit a restricted compartment and operate reliably in a humid environment.

For this project, Yilai Power worked with the customer to develop a custom lithium-ion battery pack for a portable water purifier. The engineering process covered load analysis, cell chemistry, mechanical layout, BMS protection, charger matching, documentation and prototype validation. The following case study explains the decisions involved without disclosing the customer's proprietary dimensions or electrical specification.

Why a Portable Water Purifier Needs a Purpose-Built Battery

Battery selection must begin with the purifier as a complete electrical system. Choosing a pack only by nominal voltage and amp-hour rating can overlook the short current surge required to start a pump, the combined load when several components operate together, or voltage drop at the end of discharge.

Step 1: Defining the Real Electrical and Mechanical Requirements

Before selecting cells, the engineering team clarified how the purifier would operate in normal and worst-case conditions. The required inputs included:

• nominal and loaded operating voltage;

• continuous current, maximum operating current and pump startup current;

• required runtime per charge and the duty cycle of each load;

• whether cooling or heating operates continuously or intermittently;

• maximum battery dimensions, mounting method and weight limit;

• ambient temperature, humidity, splash or water-ingress exposure;

• charging location, charging time, connector and plug type; and

• destination market and required test documentation.

This requirements-first approach is important because two purification systems with the same nominal voltage may require very different battery capacities, discharge capabilities and enclosure designs. For projects exposed to water or immersion, the complete pack, cable outlets and connectors require separate engineering evaluation. See Yilai Power's custom waterproof battery pack capabilities for those application-specific options.

Step 2: Choosing Lithium-Ion Instead of LiFePO4

LiFePO4 is often considered for industrial equipment where long cycle life and thermal stability are leading priorities. In this portable purifier, however, installation space and weight were tightly limited while the battery still needed sufficient energy and power. The team therefore selected lithium-ion cells for their higher energy density within the available pack envelope.

Samsung cells were selected for this customer project based on the agreed performance and compliance requirements. Cell brand alone does not determine pack quality: cell authenticity, matching, interconnection, thermal behavior, BMS settings and final pack validation all remain important.

Step 3: Designing a Compact and Protected Battery Structure

The available compartment required a compact arrangement of cylindrical cells. Yilai Power engineers developed a layout using cell holders and insulating epoxy-fiberglass board to support positioning, electrical insulation and resistance to movement. The mechanical structure was designed around the actual mounting space rather than forcing the customer to redesign the purifier around a standard off-the-shelf pack.

Important: operation in a humid environment is not automatically equivalent to an IP rating. If a purifier requires splash resistance, temporary immersion or continuous submersion, the required depth, duration, connector state and test method should be defined before design validation.

Step 4: Matching the BMS and Charger to the Battery

The battery management system was selected around the cell configuration and actual loads. Its current thresholds needed enough margin for pump startup and cooling-module pulses while still providing the required protection functions. Depending on the final specification, a custom pack may include overcharge, over-discharge, overcurrent, short-circuit and temperature protection.

Yilai Power also matched a charger to the battery chemistry, series configuration, maximum charge voltage and agreed charging current. The customer specified the desktop charger format, cable length, AC plug and battery-side connector. Charger protection included overvoltage, overtemperature and short-circuit protection, subject to the approved charger model and project specification.

Step 5: Planning Compliance Documentation and Testing

The project documentation plan included CE-related requirements, RoHS, REACH, CB and UN 38.3 according to the destination market and the customer's product-level compliance strategy. These items should not be treated as a single universal “battery certificate.” Their applicability depends on the battery, charger, end product, sales market and transport route.

For reference, UN 38.3 relates to testing lithium cells and batteries for transport. EU RoHS rules restrict specified hazardous substances in electrical and electronic equipment, while REACH addresses chemical substances in the EU. Final compliance requirements should always be confirmed for the complete product and target market.

Prototype validation for the portable purifier covered the agreed electrical and integration checks, including:

1. dimensional and connector verification;

2. capacity, charge and discharge checks;

3. operation under continuous load and peak-load events;

4. BMS protection-function verification;

5. charger compatibility and charging-behavior checks; and

6. on-equipment runtime and functional testing by the customer.

After sample evaluation and on-site testing, the pack operated the purification system stably and achieved a runtime above the customer's initial expectation under the evaluated test conditions.

The Final Customization Workflow

This project shows why a portable water purifier battery should be treated as an engineered subsystem. The outcome depended on understanding simultaneous loads, startup current, runtime, usable space, environmental exposure and charging—not simply selecting an 18650 pack by voltage and capacity.

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