.ut-cat{color:#333;font-family:Arial,Helvetica,sans-serif;line-height:1.5;} .ut-cat h4{color:#1a1a1a;font-size:1.15em;margin:1.5em 0 .5em;padding-bottom:.25em;border-bottom:2px solid #ccc;} .ut-cat h2{color:#1a1a1a;font-size:1.25em;margin:1.2em 0 .4em;} .ut-cat h3{color:#222;font-size:1.05em;margin:1em 0 .3em;} .ut-cat p{margin:.6em 0;} .ut-cat ul{margin:.5em 0;padding-left:1.4em;}.ut-cat li{margin:.25em 0;} .ut-cat img{max-width:100%;height:auto;} .ut-cat table{border-collapse:collapse;width:100%;margin:.5em 0;} .ut-cat th,.ut-cat td{border:1px solid #ddd;padding:6px 10px;text-align:left;vertical-align:top;} .ut-cat td strong{color:#222;} Overview The UT3550 measures battery internal resistance and voltage together using a 4-wire Kelvin connection and 1 kHz AC injection — the method that reveals a weak cell before it fails under load. It resolves internal resistance from 0.001 mΩ to 30 Ω at ±0.5% and voltage to 100 V at ±0.05%, covering everything from small consumer cells to large industrial battery banks. A 4-wire connection removes lead resistance for accuracy at low ohms, a comparison function sorts pass/fail against set limits, and results log to 500 groups with CSV export over USB-C. The IP65 body and rechargeable pack suit field and maintenance work. It's backed by UNI-T's nearly 40 years of test-meter manufacturing. Key Features AC-injection internal-resistance method (1 kHz) Internal resistance 0.001 mΩ to 30 Ω, ±0.5% Voltage 0.0001 V to 100 V, ±0.05% 4-wire Kelvin connection removes lead resistance Comparison function with pass/fail sorting Data logging to 500 groups; CSV export over USB-C Dual display (LCD & OLED); IP65 sealing Rechargeable 7.4 V 2000 mAh Li-ion UT3550 Details Internal Resistance & Voltage Together Internal resistance rises as a cell ages, often well before its open-circuit voltage drops. By measuring resistance (0.001 mΩ–30 Ω) and voltage (to 100 V) at the same time, the UT3550 flags a weakening cell while it still reads a normal voltage. 4-Wire Kelvin Accuracy A 4-wire Kelvin connection separates the current and sense paths so lead and contact resistance don't corrupt the reading — essential for the milliohm-level measurements that distinguish a healthy cell from a tiring one. Sorting & Logging A comparison function sorts cells pass/fail against set limits for fast battery-bank screening, and logging to 500 groups with CSV export over USB-C builds the record a maintenance program needs. Field Build A dual LCD/OLED display, IP65 sealing, and a rechargeable Li-ion pack make the UT3550 practical for moving down a rack of cells in the field. Applications UPS, telecom, and stationary battery-bank maintenance; testing consumer and industrial cells from small to large; incoming inspection and pass/fail sorting; and preventive programs that track internal resistance over time. Frequently Asked Questions Why measure internal resistance instead of just voltage? Internal resistance rises as a battery ages, often before voltage drops — so it catches a weak cell earlier. What is the 4-wire Kelvin method? It uses separate current and sense leads so lead and contact resistance don't affect the milliohm-level reading. Can I export results? Yes — log to 500 groups and export CSV over USB-C. Specifications DC Voltage In 100 V (0.0001 V to 100.00 V) Internal Resistance Range 0.001 mΩ to 30.00 Ω Max Resistance 30 Ω (0.001 mΩ to 30.00 Ω) Battery Voltage Range 0.0001 V to 100.00 V Battery Test Frequency 1 kHz±30 Hz Voltage Resolution 0.1 mV Measurement Resolution 0.001 mΩ / 0.1 mV Accuracy Resistance: ±0.5%rdg±5dgt , Voltage: ±0.05%rdg±5dgt Auto Ranging Yes Test Method 4-Wire Kelvin Comparison Function Yes Data Logging Yes Programmable Yes Fastest Test Rate 1/s manual range Dual Display Yes Interface USB-Type-C, USB-Device Data Storage 500 groups internal, CSV export IP Rating IP65 Display Size 3.5in Display Type Dual Display LCD & OLED Battery 7.4 V 2000 mAh Li-ion Battery Life Approx. 5h (20% brightness) Charging Time < 5 hours Ambient Temperature Range 0 °C to 40 °C Ambient Humidity 10 to 80%RH Storage Temperature -20 °C to 60 °C Battery Test Method AC Injection Documentation UT3550 Datasheet UT3550 User Manual
