How to Choose a Motorcycle Battery: What Codes Like YTX7A-BS and YTZ10S Mean

The most reliable way to choose a motorcycle battery is to match the code printed on the old battery (e.g. YTX7A-BS) exactly or with an equivalent code. The code defines size, terminal layout and technology together. Capacity (Ah) should not be lower than the original and the battery must sit snugly in its tray.

How to read a battery code

Motorcycle batteries use a widely standardised system of letters and numbers. When different brands share a code, the batteries are interchangeable in size and terminal layout.

Code part	Meaning	Example
YTX / TX	Maintenance-free (MF) AGM battery	YTX7A-BS, YTX9-BS
YTZ / TZ	Compact, high-cranking maintenance-free battery	YTZ7S, YTZ10S
YB / 12N	Conventional battery; electrolyte level needs checking	YB4L-B, 12N5-3B
Number	Capacity class and size group	7, 9, 10, 12
A, B …	Size or terminal variant within the same class	YTX7A-BS
L	Reversed terminal layout	YTX7L-BS
BS	Acid supplied separately (Bottle Supplied)	YTX9-BS
S (at the end)	Factory-activated, sealed battery	YTZ10S

The most common mistake is ignoring the “L”. A YTX7A-BS and a YTX7L-BS may be the same size, but the terminals are on opposite sides, so cables may not reach or could be connected the wrong way round.

Five checks for the right battery

1. Code: use the code on the old battery or the type in your owner's manual.
2. Terminal layout: photograph where + and − are and compare with the new battery.
3. Capacity (Ah): same or slightly higher is fine; much higher usually means a bigger case that won't fit.
4. Cranking current (CCA): determines cold-weather starting; YTZ types are strong here.
5. Dimensions: length, width and height must suit the tray and the retaining strap or bracket.

In our Batteries category you can select your motorcycle's make and model to see only compatible batteries; each product page shows the battery code and compatible models.

Preparing a dry-charged (acid pack) battery

Batteries ending in “BS” come with the acid in a separate container. Before filling they store well; once filled, the chemistry starts. The usual sequence is:

1. Place the battery on a level surface and remove the sealing strip.
2. Turn the acid container upside down so its nozzles line up with the cells and press down; let it empty completely.
3. Let the battery stand for the time the manufacturer specifies (often half an hour to an hour).
4. Press the cap strip supplied in the pack firmly into place. It is never opened again; water or acid is never added to an AGM battery later.
5. Fully charge the battery with a suitable motorcycle charger, then fit it.

Battery acid is corrosive. Wear gloves and eye protection and work in a ventilated area.

Checking the battery with a voltmeter

A basic multimeter is enough to understand the battery and charging system. Measure with the engine off and the battery rested for a few hours:

Resting voltage	Meaning
12.7 V or more	Fully charged (AGM batteries may show 12.8–13 V)
12.4 – 12.6 V	Partly charged; charging recommended
12.2 V or less	Flat; charge it, and if it keeps happening check the battery or charging system

With the engine running at mid revs you should see about 13.5–14.5 V at the battery. Below that the battery isn't charging; above 15 V it is being overcharged. In either case see our charging system (stator and regulator) guide.

Why does a battery go flat quickly?

• Short trips: the energy used for starting isn't replaced on a short ride.
• Long periods standing: alarms, clocks and ECUs slowly drain a parked bike.
• Charging faults: a failed regulator or stator either doesn't charge or overcharges and damages the battery.
• Loose or corroded terminals: weaken current flow and slow the starter.
• Extra accessories: heated grips, auxiliary lights and USB sockets can overload the charging system.

Can I fit a lithium (LiFePO4) battery?

Lithium batteries are much lighter and self-discharge slowly. However, they need a lithium-compatible charger, first-start performance can drop in very cold weather and the bike's charging voltage must suit the battery. If unsure, staying with the original battery technology is the most trouble-free option.

Making your battery last

• If the bike won't be used for more than a few weeks, connect a smart (maintenance) charger or remove the battery.
• Keep terminals clean and tight; a thin layer of terminal grease reduces corrosion.
• Don't leave the battery fully discharged; deep discharge shortens its life.
• For winter preparation, see our winter care guide.

Replacing a battery step by step

1. Switch off the ignition and disarm any alarm.
2. Disconnect the negative (−) cable first, then the positive (+). This order prevents a short if the spanner touches the frame.
3. Remove the retaining strap or bracket and lift the old battery out upright.
4. Clean the terminals and cable lugs; remove any corrosion with a wire brush.
5. Fit the new battery and connect the positive (+) cable first, then the negative (−), and tighten the bolts.
6. Refit the positive terminal cover, secure the battery and try the starter.

Old batteries contain lead and acid and must not go in household waste; take them to a battery collection point.

Frequently asked questions

Can I fit a YTX7L-BS instead of a YTX7A-BS?

Their size may be similar but the terminals are reversed. If cable length and position don't suit, it shouldn't be fitted; the right choice is a battery with the same terminal layout as the original code.

Is a higher capacity (Ah) a problem?

A slightly higher capacity is fine and gives more cranking reserve. The real limits are fitting in the tray and having the same terminal layout.

Can I use a dry-charged battery straight after filling it?

A freshly filled battery has some charge but isn't full. Fully charging it with a suitable charger before fitting improves its life and first-start performance.

Is it the battery or the charging system?

If a fully charged battery goes flat again within days and the voltage stays below 13.5 V with the engine running, the problem is most likely the charging system. If the battery won't hold a charge and its resting voltage drops quickly, it has reached the end of its life.