How to read a battery date code
Most batteries carry a short code that gives the month and year they were made or shipped. There is no single standard: each maker has its own format, and some even use different month letters. So the first step is knowing who made the battery. This table shows what each brand’s code looks like.
| Brand | Where and how it reads | Example |
|---|---|---|
| Interstate | First two characters of the code engraved on top: month letter, then the last digit of the year. It’s the shipping date [1][3] | C3: March 2013 or 2023 |
| Batteries made by Clarios (sold as many brands, including OPTIMA) | 8 characters engraved on the cover: year digit, month letter, day, shift, plant, line [4] | 5E15AHRD: May 15, 2015 or 2025 |
| Duralast, DieHard, EverStart and other store brands | The retailers don’t publish a key. Read the engraved maker’s code if there is one; a printed month/year sticker may be a store date [6][5] | 10/21: October 2021 |
| OPTIMA | First 4 digits of the 10-digit serial on the white Non-Spillable label: year digit, then day of the year [5][6] | 6086…: March 26 or March 27 of 2016 or 2026 |
| ODYSSEY | Top label: last 4 of 12 digits are month and year. Back label: month letter + year digit [7] | …0220: February 2020 |
| NorthStar | Back label: month letter (no E or I) + year digit [7] | M0: November 2010 or 2020 |
| Trojan | Negative terminal: month letter + year digit [9] | A1: January 2011 or 2021 |
| U.S. Battery | Flooded: month letter + year digit + plant letter on the positive terminal. AGM: 6 digits etched in the cover [10][11] | K4X: November 2014 or 2024 |
| Milwaukee M18 / M12 | Heat-stamped on top: year, month, day (YYMMDD), often with a plant letter [12] | 130320R: March 20, 2013 |
Month letters aren’t the same everywhere
Many codes use a letter for the month, but makers disagree about which letters. Some use A to L straight through, Clarios skips I (so J is September), and NorthStar skips both E and I. A letter from I on can therefore mean different months on different batteries. When you pick “Other brand or not sure”, the decoder shows both readings whenever they differ.
| Month | A–L: Trojan, U.S. Battery, ODYSSEY [9][10][7] | No I: Clarios [4] | No E or I: NorthStar [7] |
|---|---|---|---|
| January | A | A | A |
| February | B | B | B |
| March | C | C | C |
| April | D | D | D |
| May | E | E | F |
| June | F | F | G |
| July | G | G | H |
| August | H | H | J |
| September | I | J | K |
| October | J | K | L |
| November | K | L | M |
| December | L | M | N |
Interstate’s own FAQ lists only A = January, B = February, C = March “etc.” [1]; the decoder reads its later letters straight through the alphabet, as Batteries In A Flash lists them [6].
Made, shipped or stocked: what the date means
- Build date: Clarios, OPTIMA, ODYSSEY, NorthStar, Trojan, U.S. Battery and Milwaukee codes give the month (or day) the battery was made.
- Shipping date: Interstate’s code is the month the battery left the plant [1].
- Sticker date: a round or printed sticker is often added by the store or distributor. OPTIMA says these can differ from the build date by a year or more [5]. Interstate batteries recharged in storage carry a second code, read the same way [3].
None of them is the date the battery was sold or installed. Keep the receipt for that.
Why a code can show more than one year
Most battery codes carry only the last digit of the year, so “3” could be 2013 or 2023. The decoder lists every possible year since 2007 and leaves the choice to you: pick the one that fits when the battery was bought. Codes with a full two-digit year (ODYSSEY top labels, Milwaukee M18 and M12 stamps, U.S. Battery AGM) give one year. U.S. Battery says its AGM dates can be written day-month-year or year-month-day [10], so a code like150914 is shown both ways when the two readings differ.
Worked examples
Every example below comes from the maker’s or source’s own document and is decoded by the same code as the tool above.
| Serial | Style | How it reads | Made | Example from |
|---|---|---|---|---|
B1 | Interstate shipping-date code (month letter + year digit) | B = month letter (February); 1 = last digit of the year (2011 or 2021)Interstate's own example: February 2021. | February 2011 or 2021 | Interstate Batteries |
C3 | Interstate shipping-date code (month letter + year digit) | C = month letter (March); 3 = last digit of the year (2013 or 2023)Interstate's own example: March 2023. | March 2013 or 2023 | Interstate Batteries |
5E15AHRD | Clarios lot code (8 characters engraved on the cover) | 5 = last digit of the year (2015 or 2025); E = month letter (May); 15 = day 15 of the month; A = shift letter; H = plant (factory) letterClarios' example: May 15, 2015, first shift, Winston-Salem plant, line 4. | May 15, 2015 or 2025 | Clarios |
6J24AM9F | Clarios lot code (8 characters engraved on the cover) | 6 = last digit of the year (2016 or 2026); J = month letter (September); 24 = day 24 of the month; A = shift letter; M = plant (factory) letterCode in Clarios' photo: J is September because Clarios skips I; plant M is Middletown. | September 24, 2016 or 2026 | Clarios |
6086 | OPTIMA serial (year digit + day of the year) | 6 = last digit of the year (2016 or 2026); 086 = day 86 of the yearOPTIMA's example: made March 27, 2026. | March 26 or March 27 of 2016 or 2026 | Clarios |
7365 | OPTIMA serial (year digit + day of the year) | 7 = last digit of the year (2007 or 2017); 365 = day 365 of the yearOPTIMA's example is December 31, 2027; that date is still in the future, so only earlier decades are shown. | December 31 of 2007 or 2017 | Clarios |
4208 | OPTIMA serial (year digit + day of the year) | 4 = last digit of the year (2014 or 2024); 208 = day 208 of the yearBatteries In A Flash's example: day 208 of 2024. | July 27 or July 26 of 2014 or 2024 | Batteries In A Flash |
0755-2020 0220 | ODYSSEY top-label code (last 4 digits = month and year) | 02 = month (February); 20 = year ’20Code in EnerSys' photo: 0220 = February 2020. | February 2020 | EnerSys |
0220 | ODYSSEY top-label code (last 4 digits = month and year) | 02 = month (February); 20 = year ’20 | February 2020 | EnerSys |
K0 | ODYSSEY back-label code (month letter + year digit) | K = month letter (November); 0 = last digit of the year (2010 or 2020)EnerSys' example: November 2020. | November 2010 or 2020 | EnerSys |
M0 | NorthStar back-label code (month letter + year digit; no E or I) | M = month letter (November); 0 = last digit of the year (2010 or 2020)EnerSys' example: November 2020. | November 2010 or 2020 | EnerSys |
A1 | Trojan code on the negative terminal (month letter + year digit) | A = month letter (January); 1 = last digit of the year (2011 or 2021)Trojan's example: January 2021. | January 2011 or 2021 | Trojan Battery Company |
L2 | Trojan code on the negative terminal (month letter + year digit) | L = month letter (December); 2 = last digit of the year (2012 or 2022)Trojan's example: December 2022. | December 2012 or 2022 | Trojan Battery Company |
B4X | U.S. Battery flooded: terminal stamp (month letter + year digit + plant) | B = month letter (February); 4 = last digit of the year (2014 or 2024); X = plant (factory) letterBatteries In A Flash's example: February 2024, Corona. | February 2014 or 2024 | Batteries In A Flash |
150914 | U.S. Battery AGM: laser-etched date read as day-month-year | 15 = day 15 of the month; 09 = month (September); 14 = year ’14U.S. Battery's example: September 15, 2014. | September 15, 2014 | U.S. Battery |
140915 | U.S. Battery AGM: laser-etched date read as year-month-day | 14 = year ’14; 09 = month (September); 15 = day 15 of the monthU.S. Battery's example: September 15, 2014. | September 15, 2014 | U.S. Battery |
03/20 | Printed month/year sticker (MM/YY) | 03 = month (March); 20 = year ’20Batteries In A Flash's Duralast example: March 2020. | March 2020 | Batteries In A Flash |
0419 | Printed month/year sticker (MM/YY) | 04 = month (April); 19 = year ’19Batteries In A Flash's Duralast example: April 2019. | April 2019 | Batteries In A Flash |
130320R | Milwaukee heat stamp: year, month, day (+ plant letter) | 13 = year ’13; 03 = month (March); 20 = day 20 of the month; R = plant (factory) letterMilwaukee's example (style h): March 20, 2013, plant R. | March 20, 2013 | Milwaukee Tool |
S070628 | Milwaukee heat stamp: year, month, day (+ plant letter) | 07 = year ’07; 06 = month (June); 28 = day 28 of the monthMilwaukee's example (style f): June 28, 2007, plant S. | June 28, 2007 | Milwaukee Tool |
970210 | Milwaukee heat stamp: year, month, day (+ plant letter) | 97 = year ’97; 02 = month (February); 10 = day 10 of the monthMilwaukee's example (style c): February 10, 1997. | February 10, 1997 | Milwaukee Tool |
AXXAX0712XXXX | Milwaukee nameplate serial (characters 6–9 = year and week) | 07 = year ’07; 12 = week 12 of the yearMilwaukee's pattern: week 12 of 2007. | Week 12 of 2007 (around March) | Milwaukee Tool |
1498 | Milwaukee older packs: week and year (+ plant letter) | 14 = week 14 of the year; 98 = year ’98Milwaukee's example (style b): week 14 of 1998. | Week 14 of 1998 (around April) | Milwaukee Tool |
4297S | Milwaukee older packs: week and year (+ plant letter) | 42 = week 42 of the year; 97 = year ’97; S = plant (factory) letterMilwaukee's example (style e): week 42 of 1997, plant S. | Week 42 of 1997 (around October) | Milwaukee Tool |
80327A | Milwaukee older packs: one-digit year, month, day (+ plant letter) | 8 = last digit of the year (1988 or 1998); 03 = month (March); 27 = day 27 of the month; A = plant (factory) letterMilwaukee's example (style d): March 27, 1988 or 1998, plant A. | March 27, 1988 or 1998 | Milwaukee Tool |
50206 | Milwaukee older packs: one-digit year, month, day (+ plant letter) | 5 = last digit of the year (1985 or 1995); 02 = month (February); 06 = day 6 of the month | February 6, 1985 or 1995 | Milwaukee Tool |
What this decoder doesn’t cover
- Interstate: a longer engraved code read as supplier, month, day and year. Only Batteries In A Flash describes it, and it contradicts Interstate's own FAQ.
- Interstate: the 3-character code on the positive terminal of U-series batteries. Interstate's article mentions it but doesn't explain how to read it.
- Duralast, DieHard, EverStart and other store brands: AutoZone, Advance and Walmart's own code keys. The retailers don't publish one.
- Duralast, DieHard, EverStart and other store brands: East Penn (Deka) and Exide engraved codes. No maker document found; the only chart we found contradicts its own examples.
- OPTIMA: round stickers. OPTIMA says they are inventory stickers and can be a year or more off the build date.
- ODYSSEY: the 14-digit serial number. EnerSys uses it for traceability; it isn't a date.
- NorthStar: the 12-character serial number. EnerSys uses it for traceability; it isn't a date.
- Trojan (golf cart and deep cycle): the letter-and-number stamp on the positive terminal. Trojan's current FAQ doesn't mention it; only a how-to site reads it as an assembly date.
- Trojan (golf cart and deep cycle): Trojan lithium batteries. Trojan says they have no date code; the date is on the serial-number sticker.
- U.S. Battery (golf cart and deep cycle): a claim that the codes run one month ahead of the real build date. Only Batteries In A Flash says so; U.S. Battery doesn't.
- Milwaukee M18 / M12 tool battery: 11-character nameplate serials. No published rule; Milwaukee's bulletin covers 13-character serials only.
- Milwaukee M18 / M12 tool battery: the charge-gauge light codes. Not a published date code.
- Other brand or not sure: ACDelco, Motorcraft, Exide, Deka/East Penn, Crown, Continental, Rolls and Discover codes. We found no maker document, or only one source, for each of them.
Common questions
How do I tell how old my car battery is?
Find the date code: engraved in the plastic along the top edge of the cover, stamped on a terminal, or on a label on the side. Pick the brand above and type it in. If there is only a store sticker, it gives a rough date at best.
How do I read an Interstate battery date code?
Look down at the top of the battery near a corner for a 4–5 character code. The first character is the month (A = January) and the second is the last digit of the year: B1 is February 2021 [1]. It is the date the battery shipped from the plant.
How do I read a Milwaukee battery date code?
On M18 and M12 packs, look on top where the pack slides onto the tool for a heat-stamped number such as 130320R. Read it as year, month, day: March 20, 2013. The letter is the plant [12].
How do I read a Duralast battery date code?
AutoZone doesn’t publish a key, and Duralast batteries come from more than one maker. If the cover has an 8-character engraved code like 6J24AM9F, it’s a Clarios lot code (September 24 of 2016 or 2026). A sticker such as 10/21 is a month and year, but it may be a store date rather than the build date [5].
What does the round sticker on my battery mean?
Usually it was added by the store or distributor, for example when the battery was stocked or last checked. OPTIMA says it isn’t a reliable build date [5].
Not affiliated with Interstate Batteries, Clarios, OPTIMA, EnerSys (ODYSSEY, NorthStar), Trojan, U.S. Battery, Milwaukee Tool, AutoZone (Duralast), Advance (DieHard) or Walmart (EverStart). Brand names are used only to say which codes the decoder reads.
Sources
- Interstate Batteries (Tractor Supply store site): FAQs: How can I tell my battery's age?Used for: Interstate shipping-date code (month letter + year digit).
- Interstate Batteries: FAQs: How can I find out the lifespan of my battery?Used for: Interstate shipping-date code (month letter + year digit).
- Bumper to Bumper Radio (text written in Interstate's voice): How can I tell the age of my car battery? (Interstate Batteries)Used for: Interstate shipping-date code (month letter + year digit).
- Clarios: CPSIA certificates of compliance: lot code chart (section 6)Used for: Clarios lot code (8 characters engraved on the cover); Month letter + year digit, alphabet without I (A–M).
- OPTIMA Batteries (a Clarios brand): Where is the date code on OPTIMA batteries? (March 27, 2026)Used for: OPTIMA serial (year digit + day of the year); Printed month/year sticker (MM/YY).
- Batteries In A Flash: How to read battery manufacturer date codesUsed for: OPTIMA serial (year digit + day of the year); ODYSSEY top-label code (last 4 digits = month and year); ODYSSEY back-label code (month letter + year digit); NorthStar back-label code (month letter + year digit; no E or I); Trojan code on the negative terminal (month letter + year digit); U.S. Battery flooded: terminal stamp (month letter + year digit + plant); Printed month/year sticker (MM/YY); Month letter + year digit, alphabet with I (A–L); Month letter + year digit, alphabet without I (A–M).
- EnerSys (ODYSSEY and NorthStar batteries): Battery serial numbers and date codes (April 2021)Used for: ODYSSEY top-label code (last 4 digits = month and year); ODYSSEY back-label code (month letter + year digit); NorthStar back-label code (month letter + year digit; no E or I); Month letter + year digit, alphabet with I (A–L).
- EnerSys (ODYSSEY and NorthStar batteries): Battery serial numbers and date codes (November 2020)Used for: ODYSSEY top-label code (last 4 digits = month and year); ODYSSEY back-label code (month letter + year digit); NorthStar back-label code (month letter + year digit; no E or I).
- Trojan Battery Company: FAQs: How do I read the date code on my battery?Used for: Trojan code on the negative terminal (month letter + year digit); Month letter + year digit, alphabet with I (A–L).
- U.S. Battery Manufacturing Co.: Technical bulletin: Reading U.S. Battery Mfg. Co. date codes (3/23)Used for: U.S. Battery flooded: terminal stamp (month letter + year digit + plant); U.S. Battery AGM: laser-etched date read as day-month-year; U.S. Battery AGM: laser-etched date read as year-month-day; Month letter + year digit, alphabet with I (A–L).
- U.S. Battery Manufacturing Co.: How to read US Battery date codes (2015 sheet)Used for: U.S. Battery flooded: terminal stamp (month letter + year digit + plant); U.S. Battery AGM: laser-etched date read as day-month-year.
- Milwaukee Electric Tool Corporation: Product Support Bulletin #527: Battery pack date code, where to find, how to read (May 2013)Used for: Milwaukee heat stamp: year, month, day (+ plant letter); Milwaukee nameplate serial (characters 6–9 = year and week); Milwaukee older packs: week and year (+ plant letter); Milwaukee older packs: one-digit year, month, day (+ plant letter).
- The Garage Journal: Milwaukee M18 battery date codes (forum thread, 2012–2016)Used for: Milwaukee nameplate serial (characters 6–9 = year and week).
- Milwaukee Electric Tool Corporation: Product Support Bulletin #520: Battery pack date code (October 2010, older packs)Used for: Milwaukee older packs: week and year (+ plant letter); Milwaukee older packs: one-digit year, month, day (+ plant letter).