Battery Load Test Readings Chart: Good, Weak, Replace
This battery load test readings chart gives the voltage numbers that decide good, weak, or replace — for 12V and 24V lead-acid batteries. Bookmark it as your workshop reference.
Reviewed by Arender Siali, CECRI-trained electrochemistSAMCO Battery, Delhi12V & 24V lead-acidUpdated 9 August 2026
Quick reference: Use this battery load test readings chart as follows. Under a matched load, a healthy 12V battery holds 10.0V or above (9.6–9.9V is acceptable); below 9.0V means the battery has failed the test — recharge fully, retest, and replace if it repeats. A healthy 24V battery holds 20.0V or above (19.2–19.9V acceptable); below 18.0V means the bank has failed the test. Always test from a full charge, hold the load about 10 seconds, and read the voltage while the load is still on.
01 12V battery load test readings chart
Voltage measured while the load is applied, on a fully charged 12V lead-acid battery at the 10-second mark:
12V lead-acid — voltage under load
Voltage under load
Verdict
What it means
10.0V and above
GOOD
Holds cranking load comfortably. Battery is healthy.
9.6V – 9.9V
ACCEPTABLE
Still serviceable. Keep in use and monitor.
9.0V – 9.5V
WEAK
Borderline. Recharge and retest before deciding.
Below 9.0V
FAILED
Failed the test. Recharge fully and retest; replace if it repeats.
↔ Swipe the table sideways to see all columns
02 24V load test chart
For 24V systems — trucks, buses, some commercial equipment. If your tester works on 12V blocks, test each 12V battery separately and use the 12V chart instead.
24V lead-acid — voltage under load
Voltage under load
Verdict
What it means
20.0V and above
GOOD
Holds cranking load comfortably. System is healthy.
19.2V – 19.9V
ACCEPTABLE
Still serviceable. Keep in use and monitor.
18.0V – 19.1V
WEAK
Borderline. Recharge and retest; check both batteries.
Below 18.0V
FAILED
Failed the test. Recharge fully, retest, then test each 12V block.
↔ Swipe the table sideways to see all columns
03 Resting voltage vs state of charge
Before you load-test, the battery should be fully charged. Use this to check charge level with a multimeter at rest (no load, engine off, ideally after the battery has sat an hour):
12V & 24V lead-acid — resting voltage vs approximate charge
Resting voltage (12V)
Resting voltage (24V)
Approx. state of charge
12.6 – 12.8V
25.2 – 25.6V
~100% — ready to load test
12.5V
25.0V
~75%
12.4V
24.8V
~50% — action floor: charge before testing
12.2V
24.4V
~25% — recharge first
12.0V or less
24.0V or less
Flat — do not load test yet
↔ Swipe the table sideways to see all columns
Why this matters: A load test on a half-charged battery fails for the wrong reason — it looks like a bad battery when it is only low. Always bring the battery to full charge first, or you will condemn a good one.
04 Match the load to the battery size
The load has to be heavy enough to stress the battery. On an automotive cranking battery, use half the CCA rating printed on the label — that is the figure the test is built around. Where no CCA is marked, as on inverter, tubular and traction batteries, use roughly three times the amp-hour rating as a comparative load. Hold it for about 10 seconds. Above about 150Ah the arithmetic outruns what a portable resistive tester can dissipate, so 300A–450A is the practical ceiling. Too light a load lets a weak battery pass.
Load current vs battery size (12V lead-acid)
Battery type
Typical Ah
Load needed
SAMCO tester
E-bike / two-wheeler
12–30Ah
~60A
BCT-6 (60A)
Small / mid car
30–50Ah
~100A
LoadPro 100 (CBLT-100)
Large car / SUV
55–70Ah
~200A
BCT-200 (200A)
Inverter / tubular / solar
75–200Ah
~300A
LOAD PRO 300 (300A)
E-rickshaw traction block
100–150Ah
~300A
ERLT-300 (300A)
Truck / tractor / commercial
200Ah+
up to 450A
BCT-700 HRD (450A)
↔ Swipe the table sideways to see all columns
Above 450A: the Carbon Pile 500A takes over — an adjustable load set to half the battery's CCA and held for 15 seconds, the BCI workshop method.
Under a matched load, a 12V lead-acid battery that drops below 9.0V has failed the test. Recharge fully and retest before replacing; if the result repeats, replace it. Between 9.0V and 9.5V it is weak — recharge fully and retest before deciding.
What should a 24V system read under load?
Roughly double the 12V figures. 20.0V and above is good, 19.2–19.9V acceptable, 18.0–19.1V weak, and below 18.0V means the bank has failed the test. Recharge fully and retest before replacing. If a 24V bank fails, test each 12V block separately to find which one is at fault.
How much load should I apply?
On an automotive cranking battery, use half the CCA rating printed on the label. Where no CCA is marked — inverter, tubular and traction batteries — use roughly three times the Ah rating as a comparative load. Hold it for 10 seconds. Above about 150Ah the arithmetic outruns what a portable resistive tester can dissipate, so 300A–450A is the practical ceiling. Too light a load lets a weak battery pass; too heavy a load can fail a healthy one.
Does the battery need to be fully charged first?
Ideally test a fully charged battery — typically 12.6–12.8V at rest (25.2–25.6V for 24V). At 12.4V it is only about 50% charged and will fail a load test that a full charge would pass, so charge it further first.
How long should the load stay on?
10 seconds, and read the meter while the load is still applied. Allow about a minute of cool-down before the next test. The exception is the Carbon Pile 500A, which follows the BCI method with a 15-second load.
Does temperature change the pass threshold?
Yes. The thresholds above assume roughly 21°C. In cold weather a marginal reading may recover once the battery warms, and in hot weather the pass mark sits slightly higher. Always compare blocks at the same temperature.
Why does my battery read 12.6V but still fail?
Resting voltage only shows surface charge. A battery with sulphated or shed plates can hold 12.6V at rest and still collapse the moment current is drawn. That gap is exactly what a load test exposes.
Can I use these figures for a lithium or LiFePO4 battery?
No. This chart is for lead-acid batteries only — flooded, SMF, VRLA, AGM and tubular. Lithium chemistries have a different voltage curve and a battery management system that will cut out under a raw load.
Why does the LOAD PRO 300 show three bands instead of four?
The LOAD PRO 300 uses a simplified three-band scale on its faceplate — optimal, caution, critical — for quick reading in the field. The four-band chart here is the same data at finer resolution: its acceptable and weak bands together make up the caution range.
Which tester should I use for my battery size?
Match the load to the battery: 60A for 12–30Ah two-wheeler batteries, 100A for 30–50Ah car batteries, 200A for 55–70Ah car and SUV batteries, 300A for 75–200Ah inverter, tubular and traction batteries, and up to 450A for commercial batteries above 200Ah.
