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How to Select a Battery by Ah and CCA

What 20-hour capacity, cold cranking amps and reserve capacity mean under SAE J537, EN 50342-1 and JIS D 5301, and why ratings from different standards cannot be compared directly.

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Once the case size, terminal layout and technology are settled, starter batteries are compared on three numbers: capacity in ampere-hours (Ah), cold cranking current (CCA) and, in some markets, reserve capacity (RC). Each number is defined by a test in a standard, and the tests differ between the European, Japanese and North American standards. A figure printed on a label means little until you know which test produced it. This guide explains the definitions and how to compare batteries without mixing standards.

Capacity: the 20-hour rate

Capacity is the charge a fully charged battery can deliver under a defined discharge. For starter batteries the reference is the 20-hour rate:

  • IEC 60095-1 and EN 50342-1 define nominal capacity (C20) at 25 °C ± 2 °C, discharging at a constant current of C20 ÷ 20 until the terminal voltage falls to 10.50 V.
  • JIS D 5301:2019 uses the same basis: the 20-hour rate current to 10.5 V at 25 °C ± 2 °C.

A 60 Ah battery is therefore one that can deliver 3 A for 20 hours to 10.50 V under those conditions. It does not mean the battery delivers 60 A for one hour: capacity falls as the discharge current rises.

The 5-hour rate

Older Japanese specifications also quote a 5-hour rate capacity, which is lower than the 20-hour figure for the same battery. In GS Yuasa's technical data, for example, 46B24 is listed at 45 Ah at the 20-hour rate and 36 Ah at the 5-hour rate. JIS D 5301:2019 now keeps the 5-hour method only as a reference test. Make sure a tender and a data sheet use the same rate before comparing them. Deep cycle and traction batteries use other rates again; see the deep cycle battery guide.

Reserve capacity

Reserve capacity is the number of minutes a fully charged battery can supply 25 A before its voltage falls to 10.50 V. It represents running the vehicle's essential loads with a failed charging system.

  • JIS D 5301:2019 and IEC 60095-1 specify the test at 25 °C ± 2 °C.
  • The North American convention described in manufacturers' technical manuals uses 80 °F (about 27 °C).

RC is the second input to the JIS performance rank, alongside cold cranking current, so it is always present in Japanese ratings even when it is not printed on the label.

Cold cranking current: three different tests

All three major standards test cranking performance at −18 °C, but they apply different pass criteria:

Standard Temperature Pass criterion
SAE J537 (North America) −18 °C (0 °F) Deliver the rated current for 30 seconds with the voltage staying above 7.2 V
JIS D 5301:2019 (Japan) −18 °C ± 1 °C Voltage at 30 seconds of discharge at the rated current at least 7.2 V
EN 50342-1 (Europe) −18 °C Voltage after 10 seconds at the rated current at least 7.50 V, followed by a second discharge stage at a reduced current to 6.0 V with a minimum duration

The European test adds a sustained second discharge stage after the initial 10 seconds, while the SAE and JIS tests judge the voltage after 30 seconds. A battery that just meets one criterion at a given current will not necessarily meet the other at the same current.

Older procedures differ again. Yuasa's specification guide describes the 1999 edition of JIS D 5301 as testing at −15 °C, usually at a fixed 150 A or 300 A with voltage and duration requirements, and the older German DIN procedure as requiring at least 9.0 V after 30 seconds and at least 150 seconds to 6 V. Older batteries and labels may still carry ratings under these procedures.

Why the numbers are not comparable

Varta states plainly that if a battery's CCA rating was determined according to JIS or SAE, the figure is not comparable with a value according to EN. It also notes that a result under the old DIN procedure is only about 60% of the result under the EN procedure for the same battery. Some manufacturers publish their own approximate conversion formulas, but they describe them as dependent on battery design.

Practical consequences:

  • Compare like with like. A JIS battery rated 600 A under SAE J537 and an LN3 battery rated 680 A under EN 50342-1 cannot be ranked on those two numbers alone.
  • Ask for values under the same standard. Many data sheets give more than one rating. If not, ask the manufacturer.
  • Record the standard on the order line. "CCA 700" is not a specification; "CCA 700 A (EN 50342-1)" is.
  • Check how catalogue values were obtained. GS Yuasa's technical data, for example, notes that its SAE CCA values are based on tester readings.
  • Set testers correctly. Varta's guidance on hand-held testers is to select the standard that matches the battery's rating; otherwise the tester gives wrong results.

Cranking amps at 0 °C: CA and MCA

Some batteries, particularly marine and dual-purpose types, carry a cranking amps (CA) or marine cranking amps (MCA) rating. Odyssey (EnerSys) and Trojan define it as the current delivered for 30 seconds at 0 °C (32 °F) while maintaining at least 7.2 V. Because the test is warmer, CA and MCA figures are higher than CCA for the same battery; Yuasa describes them as typically about 25% higher. Do not compare an MCA figure with a CCA requirement.

Where ratings appear in codes

Code What it tells you about ratings
JIS (for example 80D26L) The leading number is a performance rank calculated from CCA and RC under JIS. It is not Ah or amps. See JIS battery size codes explained
ETN (for example 574 012 068) First three digits give the capacity (74 Ah); last three give EN cold cranking current divided by 10 (680 A). See the DIN/EN battery sizes guide
N-series (for example N70) For plain N types the number is broadly the 20-hour capacity in manufacturers' data; cranking current must come from the data sheet. See N-series truck battery codes
BCI group (for example 24) Size and terminal arrangement only; no rating

How to select

  1. Start from the original specification. The vehicle's original battery or the manufacturer's application data sets the minimum capacity, CCA and technology.
  2. Match or exceed capacity and CCA on the same test standard.
  3. Consider climate and duty. Low temperatures reduce available cranking performance, and vehicles with long engine-off loads need capacity and reserve capacity as much as cranking current.
  4. Do not treat higher CCA as always better. ZVEI's guidance lists cranking current that is too low as a cause of starting failure at low temperatures, but also notes that a greatly excessive value can lead to mechanical problems with the starter. Stay close to the vehicle's specification.
  5. Keep technology in view. A higher-rated flooded battery is not a substitute for a specified EFB or AGM battery on a start-stop vehicle. See EFB vs standard flooded batteries and EFB vs AGM batteries.

Common questions

Is a higher Ah battery always an upgrade?

Only if it fits the tray and hold-down, suits the vehicle's charging system and is of the correct technology.

Why does the same battery show different CCA figures in different documents?

They are often quoting different standards, or tester-based values. Ask for the standard behind each figure.

Which rating should a tender specify?

Specify 20-hour capacity and cold cranking current with the test standard named, and add reserve capacity where the fleet runs electrical loads with the engine off.

For quotations, send the size code, technology and required ratings with their standards through the battery requirement form, or browse automotive batteries and truck and bus batteries.

References

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