Lithium Battery Specs Explained: How to Read an XS Power Lithium Spec Sheet

What it is: A standardized case designation from Battery Council International, the North American body that defines automotive battery form factors.

What it tells you: Physical fit — the maximum case dimensions, the terminal type, and where the terminals sit. Nothing more. A group size is a shape, not a performance rating.

What's different about lithium: The group size tells you the battery will drop into that tray, but it no longer tells you anything about the weight or capability of what you're installing. A lithium battery in a given group can weigh a fraction of the AGM it replaces while supporting far more system wattage. Group size used to be a rough proxy for "how much battery" — with lithium, that shortcut is dead.

Practical note: Because lithium batteries are so much lighter, the factory hold-down matters more, not less. A pack that weighs a tenth of what the tray was designed to hold can move around if it isn't properly secured. Some lithium products use a spacer or bracket to fill a group-size case footprint. Secure it properly regardless.

What it is: The nominal system voltage the battery is designed to serve.

What it tells you: Which electrical system this battery belongs in — a 12V vehicle system, a 14V or 16V high-output setup.

What's different about lithium — and this trips people up: On a lithium spec sheet, the voltage figure describes system compatibility, not the literal resting voltage of the pack. Different lithium chemistries hit different cell counts and different nominal voltages, so a battery listed as serving a 12V system may rest meaningfully above 12.0 volts by design. That is not a defect and not a mislabel — it's the chemistry.

Why you care: Two reasons. First, the higher, flatter operating voltage is a genuine performance advantage: amplifiers make more power at higher supply voltage, and lithium holds that voltage under load instead of sagging the way lead-acid does. Second, voltage compatibility with your charging system is not optional. Check the listed voltage against your alternator and your amplifiers before you buy, and check the product's charging requirements before you connect anything.

What it is: The maximum instantaneous current the battery can deliver — a burst measurement, not a sustained one.

What it tells you: The battery's potential instantaneous current output under extremely low-resistance conditions. It is not a recommended operating current and should not be used to size or select a battery for a vehicle.

Why you care: A very high instantaneous-current capability generally tells you the battery has low internal resistance and can supply a large amount of current for a very short period with relatively little voltage sag. That can correlate with strong transient performance—things like starter inrush, large audio-system peaks, or other brief high-current events. But it does not tell you how much current the battery can safely sustain, how long it can support a load, or whether it is the correct battery for a particular vehicle.

Where the number becomes especially important is in electrical-system protection. If a battery is capable of several thousand amps into a fault, engineers and installers need to know that when specifying things like fuses, circuit breakers, disconnects, contactors, busbars, cable protection, and other components. Those devices need adequate interrupting capability to safely clear a fault produced by the battery.

What's different about lithium: The ratio of burst current to physical size is dramatically better. Lithium cells — LTO especially — are built to deliver bursts at many times their own capacity rating, which is how a pack that weighs single-digit pounds delivers burst current in the thousands of amps. This is the spec where the weight-to-performance gap between lithium and lead-acid is most obvious.

What it is: The actual, measured cranking output of the battery — amps delivered under a standardized sustained cranking load.

What it tells you: Real starting power, measured directly, in the battery's own terms.

Why you care: It's the honest, unconverted number. If you want to know what this specific pack does when you turn the key, this is it.

Note what's missing: You won't see a separate CCA figure the way you do on an AGM sheet. Lithium's cold-temperature behavior is governed by chemistry rather than by the plate-and-electrolyte dynamics the CCA test was designed around, so a single cranking figure plus chemistry-specific temperature guidance is the more meaningful way to rate it. Check each product's operating temperature range — this is an area where LTO and LFP behave quite differently from each other.

What it is: The cranking output of this lithium battery expressed as the equivalent AGM cranking amp rating. "Pb" is the chemical symbol for lead, so "Pb Eq" reads as lead-acid equivalent.

What it tells you: How large an AGM battery you'd need to buy to get the same real-world cranking performance.

Why the two numbers differ: Lithium holds its voltage far more steadily under a heavy load than lead-acid does. A lead-acid battery's voltage drops significantly the moment you demand serious current, which is why cranking tests are defined around a minimum voltage the battery must stay above. Lithium's flat discharge curve means it stays well above that threshold while delivering the same current — so it does more useful work per rated amp. The Pb Eq figure translates that advantage into the units you already shop in.

Why you care: This is the apples-to-apples number. If your vehicle calls for a certain CCA rating, or you're trying to figure out whether a lithium pack will out-crank the AGM currently in your truck, compare against CA Pb Eq — not the raw CA figure. Comparing a lithium battery's unconverted CA against an AGM's CA is comparing two different things and will make lithium look worse than it performs.

What it is: The battery's actual rated storage capacity — how much current it can deliver over time.

What it tells you: The literal size of the tank, in the pack's own terms.

Why the number looks small: Because on a lithium spec sheet, it's the honest number, and lithium doesn't need as many rated amp hours to do the same job. Hold that thought for the next spec.

Why you care: Amp hours matter most when the engine is off — playing music at a show, running a burp, powering accessories at a tailgate. That's all coming out of stored capacity. But taken alone, the raw Ah figure will badly mislead you if you're comparing it against an AGM.

What it is: The battery's capacity expressed as the equivalent AGM amp hour rating.

What it tells you: How many amp hours of lead-acid you'd have to buy to get the same usable energy.

Why the two numbers differ — this is the most important concept on the sheet: Rated capacity and usable capacity are not the same thing. A lead-acid battery's rated amp hours assume you drain it completely, but you can't actually do that without destroying it. Discharge a lead-acid battery deeply and repeatedly and you'll dramatically shorten its life, which is why the conventional guidance is to use only a portion of the rating.

Why you care: When you're cross-shopping against AGM, Ah Pb Eq is the comparison figure. Raw Ah against raw Ah is not a fair fight and understates what lithium actually delivers. Note also that the conversion ratio isn't a single fixed multiplier across the catalog — it varies by chemistry and by how a given product is built, which is exactly why XS Power prints the converted figure per product rather than leaving you to guess at it.

What it is: Total stored energy in watt hours — capacity and voltage combined into one figure. Conceptually, amp hours multiplied by voltage.

What it tells you: The most complete single measure of how much energy is in the pack, and the only capacity spec that's directly comparable across different voltages and chemistries.

Why it exists on lithium sheets: Amp hours alone are ambiguous once voltage varies. Two batteries with identical Ah ratings but different nominal voltages hold different amounts of energy — the higher-voltage pack holds more. Watt hours resolve that by folding voltage into the number.

Why you care: If you're comparing a 12V pack against a 14V or 16V pack, or comparing across chemistries, watt hours is the fair comparison. It's also the spec that governs runtime math: system draw in watts divided into available watt hours gets you to runtime directly, without a voltage conversion step in the middle.

Where RC went: Reserve capacity — the minutes-based endurance rating on AGM sheets — doesn't appear here. RC was designed around lead-acid's sagging discharge curve and a specific cutoff voltage. Watt hours does the same job with less ambiguity and better cross-chemistry comparability, so lithium sheets carry Wh instead.

What it is: XS Power's rating for how much total amplifier power the battery is built to support.

What it tells you: The bottom-line answer to "how big a system can this back up." It's the practical synthesis of everything above — burst current, usable capacity, and voltage stability under load, translated into the unit you actually shop amplifiers in.

What's different from AGM: AGM spec sheets split this into Primary Watts and Secondary Watts, because a lead-acid battery's capability changes substantially depending on whether it's also responsible for starting the engine and carrying the vehicle's baseline electrical load. Lithium sheets typically carry a single wattage support figure. Check each product's listing for its intended role — some are designed as main batteries, some strictly as add-on power cells, and some are rated for either.

The caveat that matters most: A battery does not make power. It stores and buffers it — the alternator generates it. Wattage support tells you what the battery can hold up under, not what your vehicle can sustain. If you're building toward a large number here, the charging system and the wiring have to scale with it. Some lithium products additionally specify a maximum alternator output they can be paired with, because their charge acceptance is high enough that an oversized alternator can push more current into them than intended. Read the product page. This is not a spec to eyeball.

What it is: Which side the positive (+) terminal sits on when you face the battery with the terminals toward you. L means positive on the left; R means positive on the right.

What it tells you: Whether your existing cables reach the correct posts. That's the whole spec — and it's still one of the most common ordering mistakes people make.

Why you care: Battery cables are cut to length. A reversed-polarity battery can drop perfectly into the tray and still leave the positive post several inches from where your positive cable ends. Best case, you're buying and running new cable. Worst case, someone forces a connection and reverses polarity on the vehicle, which can destroy an alternator, an ECU, or an amplifier in seconds.

How to check: Before you order, look at the battery you're removing in its normal installed orientation and note which side the positive cable lands on. On our lineup, reverse-polarity versions of a given model carry an R in the part number.