Resistance and continuity
Intercell connection resistance measures the small resistance of each link that joins one battery cell or unit to the next, using a low-resistance ohmmeter. A loose, corroded or poorly made link can overheat and starve the load during a discharge, so the test is a core part of acceptance and maintenance work on flooded, valve-regulated and nickel-cadmium strings.
Intercell connection resistance is the electrical resistance of the path that joins the terminal of one cell to the terminal of the next in a stationary battery string. The path includes the connector strap or cable, the bolted or welded joints at each end, any washers and hardware, and the terminal post itself. The measurement is made with a low-resistance ohmmeter, a micro-ohmmeter or a similar instrument, using a four-wire or Kelvin arrangement so that the leads do not add to the reading. It is performed on flooded lead-acid batteries, valve-regulated lead-acid (VRLA) batteries and vented nickel-cadmium batteries that supply standby or emergency direct-current power, such as substation control power, switchgear tripping, generator starting and uninterruptible power supplies. The values are tiny, so the test needs care, and it is repeated for every link in the string, including the connections to the main cables or to the rack. Published practice, including IEEE 450-2020 for vented lead-acid batteries, treats the test as a routine check of the string's physical connections.
A battery string is a series circuit, so every link carries the full discharge current. A link with extra resistance turns that current into heat, and the heating can soften terminal seals, melt a post, ignite hydrogen around a flooded cell, or in the worst case open the circuit completely in the middle of a discharge. Even short of that, the extra drop reduces the voltage that reaches the load and shortens the time the battery can support it, which can cause a protective relay or an inverter to drop out sooner than the design intended. Connection problems build slowly. Vibration, thermal cycling, creep of lead terminals and corrosion from electrolyte mist all loosen or contaminate joints, and a voltage reading at float shows nothing, because almost no current flows. That is why this test is required alongside voltage and capacity checks: it is the only routine way to find a bad link while the battery still looks healthy. It is done at acceptance to prove a clean installation and again at regular intervals to catch drift.
The measurement applies Ohm's law at very small values. A known direct current is passed through the link, the voltage drop across the connection is read with separate sense leads, and the instrument divides the voltage by the current to give a resistance. Four-wire sensing keeps the resistance of the test leads and their contact with the post out of the answer, which matters because the quantity being measured is of the same order as a poor lead contact. The result reflects the quality of the metal-to-metal joint: contact area, clamping force, cleanliness of the surfaces and any oxide, corrosion or lead creep present. Because the same material and geometry are repeated at each link in a string, the readings from sound links cluster closely, and one link that stands apart points to a local fault. Temperature changes the resistance of the metal slightly, so repeated tests are best made under similar conditions. Polarity and direction matter little, but the sense points must be placed on the same positions every time so that the result describes the same section of the path.
The test is done with the string at float or with the charger arrangement the procedure calls for, and the safety rules for stationary batteries apply: eye and face protection, insulated tools, removal of metal jewelry, an eyewash within reach, and care with the continuous energy and the possibility of arcing. The ohmmeter is chosen for low-resistance work, and its leads are checked and its calibration confirmed. Probes are placed on the terminal posts on each side of the connector so that the measured path includes the joint and the strap but nothing else, and the same positions are used on every cell. The current from the instrument is applied, the reading is allowed to stabilize, and the value is noted. Contact with the post should be firm, because a poor probe contact looks like a poor connection. Work progresses from one end of the string to the other, and the links to the output cables and to the rack are included. Where a reading is out of line, the connection is cleaned and torqued according to the manufacturer's instructions before the test is repeated, and any work done is written down together with the before and after values. The same instrument and the same probe locations are used on later tests so the numbers can be trended.
The record holds the resistance of each link in the string, identified by its position, together with the type and size of the battery, the instrument and its calibration status, the ambient and battery temperature, and the state of charge or float condition at the time. It also describes the as-found condition of the connections, for instance clean, lightly oxidized, corroded or showing signs of heating, and any cleaning, retightening or replacement done during the visit, with the readings before and after the work. These details give the next technician a baseline, because a result is meaningful mainly as a comparison with the same link on an earlier test and with its neighbors in the same string.
This page states no acceptance value. Results are judged in several ways at once. The first is comparison with the manufacturer's data for the connector and cell design, which sets what a good connection should read. The second is comparison among the links in the same string, where a link that stands apart from the typical value or from the average points to a poor joint. The third is trending against the baseline recorded at installation, where a gradual rise matters even if the link still looks acceptable. The fourth is the published guidance for the battery type: ANSI/NETA ATS-2025 and ANSI/NETA MTS-2023 call for the measurement for flooded, valve-regulated and nickel-cadmium strings in acceptance and maintenance, and IEEE 450-2020 sets out recommended practice for maintenance, testing and replacement of vented lead-acid batteries. A link that fails the comparison is cleaned, retorqued and measured again before it is accepted. For the actual limits and procedures, refer to your own licensed copies of those standards and to the battery manufacturer.
Acceptance testing sets the baseline for a new installation and is the best time to find assembly errors, such as an under-tightened bolt or a missing washer, while they are easy to correct. Maintenance testing is a trend exercise, so using the same instrument and the same probe locations matters more than any one reading. The battery type changes the details. On flooded lead-acid cells, the posts are large and accessible, and the connectors are usually bolted. On VRLA batteries, the cases are sealed and compact, the posts are smaller, and the connectors may be bolted copper bars where a clamping error shows up quickly. On vented nickel-cadmium batteries, the connectors may be flexible links or plates and the cell terminals are different, so the manufacturer's guidance on probe points and cleaning products governs. Where the string is mounted in a rack or cabinet, the connection to the rack cables and to the disconnect also belongs in the survey. Many programs pair this test with an internal ohmic measurement of each cell, which looks at the cell rather than the link.
The equipment classes and standard sections that call for this test, and the UltraDb forms that carry it.
At float almost no current flows, so a high-resistance link shows no voltage drop and every cell reads normally. The weakness appears only under a heavy load, when the link heats and drops voltage. That is why the resistance of each link is measured directly and not inferred from float voltage.
The link resistance is very small, and ordinary two-wire leads add contact and lead resistance of a similar size. A four-wire arrangement uses separate current and sense leads so that the instrument reports only the resistance between the sense points, which is the joint being checked.
Isolate and follow the manufacturer's instructions, clean the contact surfaces, retorque the hardware to the specified value, and measure again with the same probe locations. If the reading remains high, the connector or the post may need to be replaced, and the work and the before and after values are recorded.
No. The intercell test measures the link between cells, while an internal ohmic measurement looks at the condition of the cell itself. They are often done on the same visit and complement each other, since a high reading on a cell can come from a poor link nearby rather than from the cell.
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