How to Identify Car Battery Type (AGM, Flooded, Group Size)

To identify your car battery type, read the label on the top or side: it names the technology (AGM, EFB or flooded), the BCI group size and ratings such as cold cranking amps (CCA) and reserve capacity. Removable vent caps mean a flooded battery, while “AGM”, “VRLA” or “non-spillable” on the label means AGM. Your owner’s manual has the final say, because start-stop cars can require AGM or EFB. This guide shows what each marking means, how makers’ date codes differ, and what the sources say about swapping types.

Identifying Your Car Battery Type

Work through these five checks in order. Each one narrows the answer, and the last one confirms it.

1. Find the battery and the label. It is usually under the hood, but Varta says about 40% of batteries sit in the trunk and 2% inside the passenger compartment. Read the printed label before touching anything.
2. Look for type words. “AGM”, “EFB”, “VRLA”, “sealed”, “non-spillable”, “gel” or a lithium chemistry such as “LFP”.
3. Check the top. Interstate says removable vent caps or visible liquid mean a flooded battery.
4. Read the group size and ratings. The group size sets the fit; CCA and reserve capacity set the performance.
5. Match it to the owner’s manual. The manual or a vehicle lookup shows what your car was built to use.

What The Markings On The Label Mean

Marking	What it tells you	Defined by
AGM, EFB, Gel, VRLA	The battery technology. VRLA (valve-regulated lead-acid) covers both AGM and gel.	BCI glossary
Group size (24F, 35, 48)	Physical size, terminal layout and chemistry designation, so the battery fits the tray and cables.	BCI group sizes
CCA	Amps a new, fully charged battery can deliver for 30 seconds at 0 F (-18 C) while holding at least 1.2 volts per cell (7.2 V for a 12 V battery).	BCI glossary, Interstate
RC (reserve capacity)	Minutes a new, fully charged battery at 80 F (26.7 C) can supply 25 amps before falling to 1.75 V per cell (10.5 V for a 12 V battery).	BCI glossary, Interstate
Ah (amp-hours)	Stored capacity: amps times hours of discharge. Nissan notes AGM batteries add an Ah rating.	BCI glossary, Nissan
Date code	When the battery was made or shipped. The format depends on the maker (see below).	Interstate, Optima

Do not confuse CCA with CA (cranking amps, rated at 32 F) or HCA (hot cranking amps, 80 F); Interstate calls those inflated ratings. BCI adds that European EN numbers are defined somewhat differently and may not match CCA exactly.

Flooded, AGM, EFB, Gel Or Lithium: Clues That Separate Them

Type	Label and physical clues	What the maker or BCI says
Flooded (standard, wet cell)	Removable vent caps or visible liquid; usually no special wording	BCI: electrodes submerged in free-flowing electrolyte with vents; kept upright to prevent spills
EFB	“EFB” on the label or in the group size	BCI: a vented flooded battery with added design features for better cycling life, aimed at start-stop use
AGM	“AGM”, “VRLA”, “sealed” or “non-spillable” on the label	BCI: glass-microfiber separator absorbs the electrolyte, leaving no free electrolyte to spill
Gel	“Gel” or “VRLA” on the label	BCI: electrolyte immobilized with fine silica; one type of VRLA battery
Lithium-ion	A chemistry designation such as “LFP” in the group size or on the label	BCI: sealed and rechargeable; there is no single lithium-ion chemistry

One myth: no vent caps does not prove AGM. BCI defines a low-water-loss battery as a flooded design that needs no periodic watering, and Varta says almost all conventional batteries are now maintenance-free. A sealed look is a clue; the type wording on the label is the evidence. See what a flooded car battery is and what AGM car batteries are.

Lead-Acid Batteries

A 12-volt lead-acid battery has six cells, per BCI, with sulfuric acid electrolyte (Interstate says 25% to 28% acid in water). Interstate says flooded, standard, traditional and wet cell all describe a car battery that is not AGM or EFB, and lists a typical life of 3 to 5 years with regular testing after about 3 years.

EFB: an EFB looks much like a standard battery, so the label is the giveaway. Varta credits a polyester scrim around the plates and a refined active material, and says EFBs are widely used in entry-level start-stop systems.

AGM Batteries

AGM stands for absorbent glass mat. Per BCI, glass microfibers absorb and hold the electrolyte, so nothing spills. Nissan notes that AGM batteries have different charging profiles than flooded ones and often need different charger settings, and Interstate says an overcharged AGM can vent and dry out. Use a charger rated for AGM or sealed batteries.

Gel Cell Batteries

Gel batteries use electrolyte thickened with fine silica, per BCI, and are one type of VRLA battery. Interstate says the battery maker specifies the correct charge voltage for flooded, AGM or gel chemistry, so read the label before connecting a charger.

Lithium-Ion Batteries

BCI notes there is no single lithium-ion chemistry, and most need a battery management system. In BCI’s group-size system, flooded lead is the default and lithium is marked with a designation such as LFP. Interstate warns against charging lithium with a charger meant only for lead-acid batteries and suggests one with a setting marked Li.

How To Read BCI Group Size, Terminals And Date Code

Group Size And Terminal Position

BCI group sizes classify batteries by voltage, maximum overall dimensions, terminal arrangement and special features, and batteries in one group must match in size to within 2 mm. The table lists a few common passenger-car groups from BCI’s group-size sheet.

BCI group	Length x width x height (mm)	Terminal type	Terminal figure	OE CCA range
24	260 x 173 x 225	A, A2 (top)	10	200-1000
24F	273 x 173 x 229	A, A2 (top)	11F	250-900
24R	260 x 173 x 229	A, A2 (top)	11	585
34	260 x 173 x 200	A (top)	10	235-1000
35	230 x 175 x 225	A, A2 (top)	11	300-640
48	278 x 175 x 190	A, A1, A2 (top)	24	315-850
51R	238 x 129 x 223	A, A2 (top)	11	295-500
78	260 x 180 x 186	S (side)	17	465-875
94R	315 x 175 x 190	A1, A2 (top)	24	440-900

Do not guess from the number alone. Groups 24 and 24R share a listed length and width but sit under different terminal figures (10 and 11), and 24F is 13 mm longer than 24. The CCA column is BCI’s original-equipment range, for reference only. Compare post positions with the old battery before buying.

Date Code: Makers Do Not Agree

Maker	Where to look	How to read it	Example
Interstate	First two characters on the case, or the sticker	Letter = month (A is January through L for December). Digit = year, and the digit repeats every ten years.	B1 = February 2021; C3 = March 2023
Optima	Ten-digit serial on the white 1 x 3 inch “Non-Spillable” label on the side	First digit = last digit of the year. Next three digits = day of the year.	6086xxxxxx = day 86 of 2026, March 27

Interstate’s chart pairs year digit 4 with 2014 and 2024, so the digit alone never tells you the decade. Its FAQ describes the code both as the month and year of manufacture and as the ship date from the plant, and its application guide notes other imprints may differ. Optima says its round stickers are inventory stickers that may differ from the production date by a year or more. If a label fits neither pattern, ask the seller or the maker.

Start-Stop Batteries And Swapping AGM For Flooded

Replacing an AGM with a plain flooded battery is the swap the sources warn about most. Every maker below that addresses it says to follow what the car was built with.

Source	What it says
Varta	An AGM must be replaced with an AGM. An EFB can be replaced with an EFB or an AGM. A normal battery in a start-stop car leads to rapid deterioration.
Optima	A traditional flooded battery is unlikely to work very well or very long in start-stop use, and AGM is the best option when an EFB needs replacing.
Clarios	When an EFB replaces an AGM, acid stratification can make the battery management system misread the state of charge. It also says AGM suits mounting spots such as the trunk.
Interstate	Some makes require AGM and would be damaged by a traditional lead-acid battery. If the manufacturer requires AGM, the vehicle needs it.
2020 Honda Passport owner’s manual	The 12-volt battery is designed for the Auto Idle Stop model. Another type may shorten battery life and keep Auto Idle Stop from activating.

Clarios, Optima and Varta all sell AGM and EFB batteries, so weigh their comparisons with that in mind. The point they and Interstate agree on is narrow: match the type the car came with, or check with the manufacturer first.

Varta adds that start-stop batteries are linked to the car’s battery management system, so a workshop programs the system after a replacement and start-stop may not work for several hours afterward. Leave these swaps to a shop. See the best car batteries for stop-start vehicles and whether start-stop saves fuel.

Tools For Battery Identification

A flashlight and a phone photo of the label are enough for identification. A multimeter reads voltage, and Interstate’s chart ties 12.64 volts to about 75% state of charge, but voltage shows how charged a battery is, not what type it is; Interstate says to let the battery sit idle for 24 hours first. A dedicated tester such as the one in the box above adds a health check. See also how to know what type of battery your car needs.

Choosing The Right Replacement

Interstate says to follow the original-equipment specification, which you find in the owner’s manual or an application guide. Then check four things:

• Type: AGM, EFB or flooded, matching what the car requires.
• Group size and terminals: the same group and the same post positions as the original.
• CCA: the rating your vehicle calls for; Interstate notes that most engine starters come with a CCA requirement stating how much power they need.
• Lookup: BCI’s replacement database covers over 160,000 vehicles, and Interstate’s finder searches by vehicle, license plate or VIN.

For product roundups, see our car battery picks; for lifespan, how long a car battery should last.

Battery Handling Safety

Interstate warns that lead-acid batteries contain explosive hydrogen-oxygen gases and sulfuric acid that can cause severe burns. Its precautions: wear eye, face and hand protection; ventilate the work area; never lean over a battery while jump-starting, testing or charging; keep flames and sparks away; and remove hand and wrist jewelry. If electrolyte splashes into an eye, flood it with clean, cold water for at least 15 minutes and get prompt medical attention. See also which terminal to disconnect first and how to jump-start safely. If the case is cracked or swollen, or the car is a start-stop model, have a shop handle it.

Keep reading

• Car Battery Replacement Cost (2026): Flooded vs AGM Prices
• AGM vs Lithium Car Battery
• Best BMW Battery: Top AGM Picks by Group Size (49, 94R & Auxiliary)

Frequently Asked Questions

How Can I Tell What Type Of Battery I Have In My Car?

Read the label on the top or side of the battery. It should show the technology (AGM, EFB or flooded), the BCI group size and ratings such as CCA. If it is missing or unreadable, check the owner’s manual or a vehicle lookup.

How Do I Know If My Car Battery Is Agm Or Standard?

Interstate says to check the label for “AGM” or the words “sealed”, “non-spillable” or “VRLA”. Removable vent caps or visible liquid mean a flooded (standard) battery. Some flooded batteries are maintenance-free, so the label wording beats a missing cap.

How To Identify Types Of Batteries?

For a 12-volt car battery, the main types are flooded lead-acid, EFB, AGM, gel and lithium-ion. BCI treats flooded lead as the default and marks the others with a designation such as EFB, AGM or LFP.

How Do I Find My Car Battery Code?

Code can mean the BCI group size (such as 24F), the date code on the case or sticker, or the maker’s serial. Optima prints a ten-digit serial on a white side label; Interstate stamps a letter-and-digit date code on the cover.

Can I Find My Battery Type From My License Plate or VIN?

Interstate’s battery finder searches by vehicle, license plate or VIN. For vehicles with more than one battery configuration, Interstate says PR codes are on a tag near the spare tire or in the warranty booklet.

Does My Car Have a Lead-Acid or Lithium Battery?

BCI’s group-size system assumes flooded lead unless a designation says otherwise, and lithium is marked with a chemistry such as LFP. Check the label and owner’s manual, and match the charger to the chemistry.

What this guide does not cover: battery prices, brand rankings and vehicle-specific fitment. Use your owner’s manual or a retailer lookup for those. This page is general information, and the owner’s manual takes precedence.