In short
- The quickest way to choose the right one is to check the label on your current battery: the battery part number (YTX9-BS, YTZ10S, YB12AL-A2...) sums it all up.
- Check the dimensions, polarity and terminals: the replacement must never be larger than the original, and the positive terminal must be on the same side.
- Cold cranking amps (CCA) and capacity (Ah) should match or be higher. Compare ratings using the same standard (EN or SAE) and the same hour rate (10 h or 20 h).
- AGM is the all-round choice. Lithium is a lightweight option for summer, but it is not suitable for extreme cold or lead-acid chargers with desulphation mode.
- If you replace a conventional battery with an AGM, the voltage regulator / rectifier must charge between 14.0 and 14.8 V.
Replacing a motorcycle battery is straightforward when you find the right battery part number, and frustrating when you don’t: the cables won’t reach, the cover won’t close or the motorcycle won’t start on the first cold morning. The good news is that almost all motorcycle batteries use the same naming system, created by Yuasa, and you can work out what you need with the label from your current battery and a tape measure.
This guide takes you through where to find the battery part number, how to read it, how to measure the battery if there is no label, which figures matter, which technology to choose, and how to charge and store your battery so it lasts.
Where to find your battery part number
- On the label of your current battery. This is the most reliable source if it is the original battery. The battery part number is on the front or the lid (YTX12-BS, YTZ10S, YB14L-A2, 12N9-4B-1...) and is almost always accompanied by the Ah rating and hour rate ("10HR" or "20HR"), as well as the starting current.
- In your motorcycle’s manual, under specifications or electrical system: for example, “YTZ10S, 12 V 8.6 Ah”.
- In the motorcycle manufacturer’s spare parts catalogue (the dealer’s microfiche).
- In the battery compartment. There may be a sticker showing the battery type or a polarity diagram.
Take a photo before removing the battery
Before removing the battery, take a photo of the label and the cable connections. That way, you’ll have a record of the battery part number and which side the positive terminal is on, even if the label is damaged when you take it out.
One thing to bear in mind: if your current battery is not the original, someone may have fitted the wrong one before. Yuasa points this out in its technical manual: copying the battery that is already fitted without checking it can repeat the same problem. If in doubt, check your motorcycle’s manual.
How to read a battery code (YTX9-BS, YTZ10S, YB12AL-A2)
Yuasa’s system is not an official standard, but the whole industry uses it as a common language: other manufacturers change just the first letter (GS uses GTX, Exide uses ETX and BS Battery uses BTX) and leave the rest the same. Here’s how to read it:
| Part | What it means | Example |
|---|---|---|
| Y | Yuasa’s brand letter (other brands use their own letter) | YTX9-BS |
| YTX | Maintenance-free AGM series | YTX14-BS |
| YTZ | High-performance AGM: more starting power in a compact case; always factory-activated | YTZ10S |
| YT | Maintenance-free AGM with a different case family | YT12B-BS |
| YB | High-performance conventional flooded battery (YuMicron series) | YB9-B |
| 12N / 6N | Standard conventional battery; the first number is the voltage (12 or 6 V) | 12N12A-4A-1 |
| The number | For YTX, YTZ and YT, it indicates size and power; for YB, 12N and 6N, it is close to the Ah rating | YTX9-BS (8 Ah) |
| L | Reversed polarity: positive terminal on the right | YTX7L-BS |
| H | More starting power in the same case | YTX20HL-BS |
| A, B after the number | Case variant: they are not interchangeable | YTX7A-BS ≠ YTX7L-BS |
| -BS | Supplied dry, with a separate acid bottle | YTX9**-BS** |
There are two practical points to remember. First, a higher number does not guarantee a larger case: a YTZ10S and a YTX9-BS are a similar size, but they are not the same battery. Second, the battery part number tells you the family, but the dimensions, polarity and terminals are what matter. Each battery part number page includes a diagram showing all three.
How to measure the battery and check its polarity
If the label has worn off or you want to make sure a replacement will fit, measure the old battery:
- Length: the longest side, with the battery’s label facing you.
- Width: from the front face to the back.
- Height: from the base to the highest point, including the terminals.
- Polarity: with the label facing you and the terminals at the top, check which side the + is on.
The golden rule is that the replacement must not be larger than the original in any dimension. A few millimetres less can be made up with a foam pad; a few millimetres more may stop the seat from closing or cause a terminal to touch metal. Yuasa specifies its dimensions with a tolerance of ±1.6 mm.
Also check the terminal type (AGM batteries usually have a tab terminal with bolt and square nut; small conventional batteries have a side terminal) and, on conventional batteries, which side the vent tube comes out of. For a step-by-step guide, see how to test your motorcycle battery.
The figures that matter
Voltage: 6 or 12 volts
Almost all modern motorcycles use 12 V (six cells of around 2 V each). Older mopeds, some Vespa models and classic motorcycles use 6 V (three cells). Never fit a 12 V battery where a 6 V battery belongs, or vice versa.
Capacity (Ah) and the hour rate
Amp-hours measure how much energy the battery stores. The figure is given with an hour rate: 10HR (C10) or 20HR (C20). The same battery has a higher rating at 20 hours: a YTX20HL-BS is rated at 18 Ah at the 10-hour rate and 18.9 Ah at the 20-hour rate. When comparing brands, always compare batteries at the same hour rate. More Ah than the original is not a problem: it gives you extra reserve.
Cold cranking amps (CCA): EN and SAE ratings
This is the current the battery delivers at −18 °C. Two test methods give different figures for the same battery:
- EN (European): the current it can maintain for 10 seconds without dropping below 7.5 V.
- SAE (American): the current it can maintain for 30 seconds without dropping below 7.2 V.
Do not compare the two standards directly: compare EN CCA with EN CCA. The original battery’s CCA is the minimum; higher CCA gives you extra reserve in winter, which is useful for large-capacity, high-compression motorcycles.
Conventional, AGM, gel or lithium
| Conventional | AGM | Gel | Lithium (LiFePO4) | |
|---|---|---|---|---|
| Maintenance | Check the level and top up with distilled water | None; never open it | None | None |
| Vent tube | Yes | No | No | No |
| Position | Upright only | Upright; factory-activated batteries can be tilted | More tolerant | Depends on the manufacturer |
| Self-discharge | High: charge every month when not in use | Low: charge every 3 months | Low | Very low |
| In cold weather | Adequate | Very good | Good | Poorer: starting power drops significantly |
| Charger | Lead-acid, no more than 3 A | Smart motorcycle charger | Smart motorcycle charger | Lithium-specific |
AGM is the all-round choice: it never needs topping up, loses little charge when left unused and does not spill, making it ideal for motorcycles left standing for weeks, scooters, quad bikes and personal watercraft (PWC). Many batteries sold as “gel” motorcycle batteries are actually AGM inside.
Switching from conventional to AGM
If your motorcycle has a conventional battery (YB, 12N) and you want to fit an AGM, check that the voltage regulator / rectifier charges between 14.0 and 14.8 V (measure at the terminals with the engine running at 3.000–4.000 rpm). Some older motorcycles charge below this range, so a conventional battery is the only option. If your motorcycle has an electrolyte level sensor, it is specific to conventional batteries and is not used with an AGM.
Lithium batteries are much lighter and can sit for months without discharging, but they have limitations. They are not suitable for snowmobiles or regular use below freezing, motorcycles with a voltage regulator / rectifier that charges above 15 V, motorcycles with parasitic drain (alarm, GPS) that are left for months without a battery maintainer, classics with a dynamo or poor regulation, or situations where your only charger is a lead-acid charger with desulphation mode. They must not be charged below 0 °C unless their electronics manage this. We compare the options in AGM, gel or lithium.
Factory-activated or supplied with an acid pack
- Factory-activated (FA, “ready to fit”): it comes filled, sealed and charged. Fit it straight away; it is only worth checking the voltage and giving it a top-up charge if it is below 12.8 V. YTZ batteries are always sold this way, as are Satkit’s OUTDO AGM batteries.
- Supplied with an acid pack (-BS): it comes dry, with the acid in a separate container. Unopened, it can be stored indefinitely. Once opened, it needs to be filled, charged and fitted.
If your battery comes with an acid pack, follow these steps:
- Work off the motorcycle, on a flat surface in a well-ventilated area, wearing goggles and gloves. Never activate or charge the battery while it is fitted.
- Use only the acid supplied with the battery: it is more concentrated than the acid in a conventional battery.
- Check that the aluminium seal is intact, then remove it.
- Take the cap strip off the container and keep it: this is the permanent cover.
- Place the container upright over the six openings and press down to break the seals, without tilting or squeezing it.
- Let it drain completely (around 30 minutes for 3 to 12 Ah batteries and 60 minutes for batteries over 12 Ah), then leave it to stand for 2 hours.
- Initial charging is essential: when newly filled, the battery is at 75–80%. Use a smart charger or charge at the current shown on the label (Ah divided by 10, never more than 3 A).
- Switch off the charger before removing the clamps.
- Press the cap strip into place with both hands; do not use a hammer. Never open it again or add water.
- Wait an hour, check the voltage and fit the battery, connecting the positive terminal first.
How to charge your battery
- Use a smart motorcycle charger, rated at no more than 3 A. High-current car chargers can damage small batteries.
- Recommended current: Ah divided by 10 (for a 12 Ah battery, use 1.2 A).
- A smart charger can stay connected to an AGM indefinitely; uncontrolled trickle chargers cannot.
- If the voltage drops below 11.5 V, the battery is heavily discharged and needs a charger with a recovery mode. If the voltage does not rise after 30 minutes of charging, it needs to be replaced.
- Check the charging system: with the engine running at 3.000–4.000 rpm, the voltage at the terminals should be between 13.0 and 14.5 V. If it stays the same as when the engine is off, the voltage regulator / rectifier or alternator is faulty, and a new battery will eventually go flat too.
Short journeys of less than 25–30 km do not fully recharge the battery, and parasitic drain can flatten it: a 7 mA draw takes around 60 days to bring it down to half charge; at 30 mA, it takes just 14 days. Find out more in how to charge and store your motorcycle battery.
Storing your motorcycle over winter
- Charge it fully before storing it.
- Leave a smart battery maintainer connected or disconnect the negative terminal (or remove the battery).
- If you do not have a maintainer, check the voltage every month: charge it if it falls below 12.4 V. Charge it every 3 months regardless.
A cool place is better than a warm one: at 10 °C, the voltage drops by around 0.1 V per month, and the rate doubles for every additional 10 °C. Take care in freezing weather, too: a charged battery will not freeze, but a discharged one can freeze close to 0 °C and crack.
Checking the voltage with a multimeter
Check the resting voltage: after charging, leave the battery unused for an hour (or switch on the ignition for 3 minutes and wait 10) to remove the surface charge.
| State of charge | AGM (YTX, YTZ) | Conventional (YB, 12N) |
|---|---|---|
| 100% | 12.8–13.0 V | 12.6 V |
| 75% | 12.5–12.8 V | 12.4 V |
| 50% | — | 12.1 V |
| 25% | — | 11.9 V |
| Discharged | Below 11.8 V | Below 11.8 V |
Remember these three thresholds: below 12.4 V, charge it now; below 11.5 V, it is deeply discharged; with the engine running, 13.0–14.5 V is the correct range. This table does not apply to lithium batteries: their resting voltage should be 13.0 V or higher.
How to tell if your motorcycle battery is dead
Typical signs include a starter motor that turns slowly or only clicks; dashboard lights that flicker or reset when starting; a battery that needs frequent charging; a swollen, misshapen or leaking case; the battery getting hot while charging; or sulphate on the terminals.
The definitive test: fully charge the battery, let it rest, then connect a multimeter while operating the starter. If the voltage drops below 9.5 V, the battery needs to be replaced. Find out more in how to tell if your motorcycle battery is dead.
When an alternative battery part number will fit
A battery with a different part number will fit if it passes these five checks:
- Dimensions: the same or smaller in all three dimensions. Never larger.
- Polarity: the positive terminal is on the same side.
- Terminals: the same type and in the same position (and, for a conventional battery, the vent is on the same side).
- Ratings: the same voltage, and CCA and Ah ratings that match or exceed the original, compared using the same standard and hour rate.
- Technology: compatible with the charging system (conventional to AGM only if the voltage regulator / rectifier charges at 14.0–14.8 V).
The most common example is the same case with more starting power: the YTX20HL-BS fits in the same space as the YTX20L-BS and delivers more current. The most common mistake is the same case with the polarity reversed: the YTX14-BS and YTX14L-BS have the same dimensions, but the cables will not reach or, worse, may be connected the wrong way round.
Which battery for each type of vehicle
| Vehicle | What it needs | What to fit |
|---|---|---|
| Road motorcycle | Starting power suited to the engine size; modern sports bikes use compact cases | AGM; YTZ if that is the original battery |
| Scooter and moped | Long periods unused and short journeys | Sealed AGM, due to its low self-discharge |
| Classic motorcycle | Older voltage regulator / rectifier, sometimes 6 V | Conventional; AGM only if it charges at 14.0–14.8 V |
| Quad bike | Vibration, mud and possible rollovers | Factory-activated AGM: it will not spill and can be tilted |
| Personal watercraft (PWC) | Moisture, salt and months out of use | Sealed AGM and anti-corrosion protection on the terminals |
| Snowmobile | Starting below freezing | Prioritise CCA, keep it charged and do not use lithium |
| Lawn mower or garden tractor | Seasonal use and modest starting demands | Conventional or AGM; charge it before the season starts |
Common mistakes
- Buying a battery with the opposite polarity (YTX14-BS instead of YTX14L-BS): the cables will not reach or may be connected the wrong way round, blowing fuses or damaging the voltage regulator / rectifier or ECU.
- Getting the height wrong: it fits lengthways and widthways, but catches on the seat or a terminal touches metal.
- Fitting one with lower CCA than the original: it starts in summer but leaves you stranded in winter.
- Comparing SAE CCA with EN CCA, or 20-hour Ah with 10-hour Ah.
- Skipping the initial charge for a -BS battery, or filling it with water or acid from another battery.
- Removing the caps from an AGM to “top it up”.
- Charging it with a 10 A car charger.
- Fitting an AGM to a motorcycle with low charging voltage (classic motorcycles).
- Using a charger with desulphation mode on a lithium battery, or leaving a lithium battery for months with parasitic drain.
- Replacing the battery without checking the voltage regulator / rectifier: the new one will end up the same way.
- Fitting a -BS or conventional battery on its side.
- Blocking the vent on a conventional battery or failing to remove its red cap.
Recycling
A motorcycle battery is a starting, lighting and ignition (SLI) battery under European Regulation 2023/1542, which replaced the old Batteries Directive. Never put it in the bin: take it to a shop, garage or recycling centre. Shops that sell starting batteries must accept used batteries of that type free of charge. Its label displays the crossed-out wheeled bin and the Pb (lead) symbol.
Frequently asked questions
Can I fit a battery with more Ah than the original?
Yes, as long as the dimensions, polarity and terminals match. More capacity simply gives you extra reserve, both for starting and for when the motorcycle is left unused.
What about one with more CCA?
That is fine too, provided the same conditions are met. More starting current gives you extra reserve in winter; the motorcycle only draws what it needs.
What does -BS mean on a motorcycle battery?
It means the battery is supplied dry, with a separate acid pack. You need to fill it and complete the initial charge before fitting it.
Do I need to charge a new factory-activated battery?
It is not essential. Check the voltage: if it is 12.8 V or higher, fit it as it is; if it is lower, give it a top-up charge with a motorcycle charger.
How long does it take to charge?
It depends on how discharged the battery is and the charging current. As a guide, Yuasa estimates around 8 hours to charge a YTX14 from 50% to 100% with a 1 A charger.
Can I use a car battery in a motorcycle?
No. It will not fit, its charging current and construction are not suitable for a motorcycle, and it is not designed to withstand motorcycle vibration.
Can I fit a battery on its side?
Only if it is factory-activated and non-spillable, such as a sealed AGM. A conventional or -BS battery must always be upright.
Satkit battery
OUTDO UTX9-BS
12 V, 9 Ah battery with 135 A cold cranking amps, a replacement for the YTX9-BS. Factory-activated and charged, ready to fit. Positive terminal on the left.
Where to buyfrom €24.35
Prices incl. VAT checked on 7 October 2026; they may change.
OUTDO HCZ10S-MF
12 V, 9 Ah battery with 170 A cold cranking amps, replacing the YTZ10S. Factory-activated and charged, ready to fit. Positive terminal on the left.
Where to buyfrom €32.48
Prices incl. VAT checked on 7 October 2026; they may change.
OUTDO UTX7L-BS
12 V, 7 Ah battery with 75 A CCA, replacing the YTX7L-BS. Supplied factory-activated and charged, ready to fit. Positive terminal on the right.
Where to buyfrom €20.28
Prices incl. VAT checked on 7 October 2026; they may change.
OUTDO UTX14-BS
12 V, 12 Ah battery with 200 A cold cranking amps, compatible with the YTX14-BS. Factory-activated and charged, ready to fit. Positive terminal on the left.
Where to buyfrom €36.54
Prices incl. VAT checked on 7 October 2026; they may change.
Sources
- Yuasa, technical manual for motorcycle and recreational vehicle batteries (in English)
- GS Yuasa, commissioning and care of motorcycle batteries (in English)
- Shorai, LFX lithium battery manual (in English)
- Battery University, charging at high and low temperatures (in English)
- Regulation (EU) 2023/1542 on batteries and waste batteries
