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P1 and P2 are the same T-king YR1035 instrument in different sets, and their listings publish the most measurement detail of the three: a 1 kHz AC sinusoidal four-wire method, a range to 200 ohms, 0.01 milliohm resolution, and a ZR mode claimed to reach 0.30 to 0.50 milliohms. P3 is a YAOREA YR1035+ that the listing describes as a true four-wire system measuring resistance and voltage together, but it publishes no range or resolution figures at all. For maintenance work where you need to know whether a reading is meaningful, P1 or P2 is the pick because the listing states the resolution floor; choose between them on which set contents suit your bench. P3 is the pick only if you can obtain the missing specifications before buying.
Why four wires, and why 1 kHz, decide whether the reading means anything
Internal resistance in a lead-acid, lithium or NiMH cell is measured in milliohms, and often in single-digit milliohms. A two-wire ohmmeter pushes current through the same leads it uses to sense voltage, so the resistance of the leads, the probes and the contact patch between probe tip and terminal is added to the battery. On a healthy 12 V battery the true internal resistance might be 5 milliohms; a pair of test leads and a mediocre contact can add 20 milliohms or more. The error is larger than the quantity.
A four-wire, or Kelvin, connection separates the current-carrying pair from the voltage-sensing pair. Current is injected through one set of leads; voltage is sensed through a second set that carries almost no current, so the voltage drop across the sense leads is negligible. What remains is the voltage developed across the battery’s own internal impedance. This is why the listings for P1 and P2 state the four-wire method explicitly: it is the mechanism that makes a milliohm reading possible at all.
The 1 kHz AC part matters too. A DC resistance measurement polarises the cell and reads a value that depends on how long you hold the probes down. A small AC signal at 1 kHz does not polarise the cell in the same way and gives a repeatable number that can be compared between readings and between cells. The P1 and P2 listings state a true four-line 1 kHz AC sinusoidal method. P3’s listing states a true four-wire testing system but does not name the test frequency.
None of this is exotic. It is the reason a battery internal resistance tester is a different instrument from a multimeter, and the reason milliohm meters for low resistance testing exist as a separate category.
The comparison table: what these three listings publish, and where they go quiet
| Specification | P1 (T-king YR1035 Set A) | P2 (T-king YR1035 Set D) | P3 (YAOREA YR1035+) |
|---|---|---|---|
| Measurement method | Four-wire, 1 kHz AC sinusoidal (stated) | Four-wire, 1 kHz AC sinusoidal (stated) | True four-wire system (stated); frequency not stated |
| Resistance range | Up to 200 ohms (stated) | Up to 200 ohms (stated) | Not stated in the listing bullets |
| Resolution | 0.01 milliohm minimum (stated); ZR mode 0.30 to 0.50 milliohm (stated) | 0.01 milliohm minimum (stated); ZR mode 0.30 to 0.50 milliohm (stated) | Not stated in the listing bullets |
| Voltage measurement | Not stated in the listing bullets | Not stated in the listing bullets | Measures voltage simultaneously (stated) |
| Display | Digital LCD with backlight (stated) | Digital LCD with backlight (stated) | Large LCD, real-time results (stated) |
| Intended use | Battery internal resistance measurement (stated) | Battery internal resistance measurement (stated) | Battery performance testing, screening and configuration (stated) |
Cells marked “Not stated” mean the listing does not publish that figure. They are not estimates and should not be treated as zero.
Read the table as a map of confidence, not as a ranking. P1 and P2 give you enough to know what the instrument can resolve. P3 tells you the architecture but not the numbers, which means you cannot tell from the listing alone whether it will resolve the difference between a 3 milliohm cell and a 6 milliohm cell.
The three instruments, and what their listings actually say
T-king YR1035 (Set A)
The listing publishes the measurement method, the range and the resolution, which is the minimum you need to judge whether a milliohm reading is real.
T-king YR1035 (Set D)
Functionally the same instrument as P1 with the same published figures; the difference is the set contents, so choose on which accessories you need rather than on measurement capability.
YAOREA YR1035+ (Combination 2)
A four-wire resistance and voltage tester that the listing describes as suitable for field and bench work, but it omits the range and resolution figures needed to compare it properly.
The resolution floor is the specification that decides the job
Range and resolution are different things, and the listing for P1 and P2 makes the distinction unusually clearly. The range is up to 200 ohms. The resolution is 0.01 milliohms, with a special ZR mode claimed to reach 0.30 to 0.50 milliohms. A wide range lets you measure a whole string or a large cell; a fine resolution lets you see a change in a small cell.
In maintenance practice, the second number is usually the one that matters. You are rarely asked for the absolute internal resistance of a cell. You are asked whether this cell has changed since the last reading, or whether it is worse than its neighbours in the same string. A cell that has drifted from 4 milliohms to 8 milliohms is a problem. An instrument that resolves to 0.01 milliohms can show that drift; an instrument that only resolves to 1 milliohm can show it too, but with much less margin for the trend. The ZR figure of 0.30 to 0.50 milliohms is the listing’s claim about the smallest resistance the instrument can usefully indicate, and it is worth reading as a claim rather than a guarantee. It is plausible for a four-wire AC instrument; it is not something a two-wire meter can approach.
Where a listing is silent on resolution, as P3 is, you cannot make that judgement. The honest position is that P3 may be perfectly capable, but the listing does not let you compare it on the specification that matters most. If you are buying for a maintenance programme where you will trend readings over months, ask for the resolution figure before you commit.
What the listings do not say about voltage, temperature and the rest of the job
Internal resistance is temperature-dependent. A battery measured cold will read higher than the same battery measured warm, and the difference can be large enough to look like a fault. None of these three listings publishes a temperature compensation feature or a temperature measurement function. That does not mean the instruments lack one; it means the listings do not say. If you plan to compare readings taken in an unheated plant room in winter with readings taken in summer, you need to know how you will handle that, and the listing will not tell you.
Voltage is the other gap. P3’s listing states that it measures internal resistance and voltage simultaneously. P1 and P2’s listings do not state a voltage function in the bullets supplied, even though the instrument class normally includes one. Treat that as a listing gap, not as a confirmed absence. If you need to record open-circuit voltage alongside resistance in a single pass, P3’s listing is the only one of the three that says so explicitly.
The listings also do not describe the probe or clip type in enough detail to judge contact quality, which is the practical limit on repeatability. A four-wire instrument is only as good as its Kelvin connection. If the clips do not sit flat on the terminal, or the probe tips do not bite through surface oxide, the reading will wander. This is the maintenance nobody mentions: clean the terminals, check the clips, and take the reading the same way every time. The instrument cannot fix a bad contact.
For a broader view of how resistance testing fits alongside other electrical checks, see insulation resistance testers and electrical testers. Internal resistance and insulation resistance are different measurements on different parts of the system, and confusing them leads to the wrong tool.
Where a battery internal resistance tester stops being the right instrument
An internal resistance tester tells you about the impedance inside a cell. It does not tell you the state of charge, it does not perform a capacity test, and it is not a load bank. A cell can have a normal internal resistance and still be undercharged, and a cell can have a high internal resistance and still hold a surface charge that makes a voltmeter read healthy. If your question is how much energy the battery actually stores, you need a capacity test, not a resistance test. The two are complementary.
It is also not a substitute for a proper load test on a starting battery, and it is not a substitute for a battery monitor on a working system. A resistance tester is a diagnostic instrument for comparing cells and tracking change. If you are commissioning an off-grid bank and want to know what is going in and out, a monitor is the right tool; see how to choose a battery monitor for an off-grid system.
Finally, the instrument is only one part of the procedure. The reading depends on the contact, the temperature, the state of charge at the time of measurement, and the consistency with which you repeat the test. A maintenance programme built on irregular readings from a good instrument is worth less than a programme built on regular readings from a modest one. Buy the instrument that publishes its resolution, then write down how you will take the reading before you take it.
Recommended Tools
Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.
Frequently Asked Questions
Can I use an ordinary multimeter to measure battery internal resistance?
Not usefully. A two-wire multimeter includes the resistance of its leads and the probe contact in the reading, and on a battery that is often larger than the internal resistance itself. A four-wire instrument separates the current path from the sensing path so the leads drop out of the measurement. That is the whole reason this instrument class exists.
P1 and P2 look identical. Is there any measurement difference?
The listings publish the same measurement figures for both: four-wire, 1 kHz AC sinusoidal, range to 200 ohms, 0.01 milliohm resolution, ZR mode 0.30 to 0.50 milliohms. They are different sets of the same instrument. Choose on the accessories included in the set, not on the measurement specification.
Why does the listing for P3 not give a range or resolution?
The listing bullets supplied describe the four-wire system, the display, the use cases and the portable design, but they do not publish range or resolution. That is a gap in the listing, not evidence that the instrument lacks those capabilities. If those figures matter to you, ask the seller before buying.
What does the ZR mode on P1 and P2 actually claim?
The listing states that pressing HOLD enables the ZR function to measure internal resistance as low as 0.30 to 0.50 milliohms. That is the listing's claim about the low end of the measurement capability. It is a useful figure because it tells you the instrument is intended for small cells, not just large ones, but it is a manufacturer claim and not an independently verified number.
Do these testers measure voltage as well as resistance?
P3's listing states that it measures internal resistance and voltage simultaneously. P1 and P2's listings do not state a voltage function in the bullets supplied. That does not prove the function is absent, but if voltage recording in the same pass is important to you, P3 is the only one of the three whose listing says so.
Is internal resistance the same as capacity?
No. Internal resistance is an impedance measurement that indicates how easily the cell delivers current and how it is ageing. Capacity is the amount of charge the cell can store and deliver. A cell can have acceptable internal resistance and reduced capacity. Use a resistance tester for comparison and trending, and a capacity test when you need to know stored energy.
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