Everything about motorcycle batteries

Table of contents

Everything about motorcycle batteries


Everything about motorcycle batteries

Battery science for everyday life
Tension issue

Nothing would work without the motorcycle battery. Only the small, inconspicuous part, usually found under the seat, breathes life into the bike. But what are the differences, what needs to be considered when buying and maintaining?

There is a lot of tension in the subject.

Jorg Lohse


Because modern motorcycles usually do not have a kick starter, first-class maintenance and care of the starter battery is the order of the day. Now, as an attentive reader of brochures, you say: “The next time my battery died, I wanted to use a maintenance-free type anyway.” But that doesn’t solve all your problems. Because maintenance-free does not mean free of maintenance.

Which does ______________ mean “maintenance free”?

Maintenance-free only refers to the fact that the acid level no longer needs to be checked. In fact, it can no longer be controlled at all. The housing of a maintenance-free battery – recognizable by the abbreviation MF – is not transparent in contrast to conventional lead-acid batteries, and after the first filling with sulfuric acid, the individual cell openings are permanently sealed with plugs. The acid is either absorbed in special glass fiber or fleece mats, other types use silica, which solidifies the battery acid in gel form. For the former type, the designation AGM (Absorbed Glass Mat) can be found on the housing. Gel batteries are currently not that widespread. One manufacturer is Mareg, a subsidiary of Exide, one of the world’s largest battery producers. These gel types have been used in BMW motorcycles, among others, since 2002.

Regular charging is also important for maintenance-free batteries. It is true that MF types store energy better than normal starter batteries during the storage period. But they are also not immune to self-discharge, which is a temperature-dependent, chemical reaction process without connection to a consumer, whereby the frequency is halved compared to standard batteries. A cold location should be selected for longer periods of standstill, as rising temperatures accelerate self-discharge. On average, a starter battery with a capacity of twelve ampere hours (Ah) has already lost a third of its capacity after two months and should then be recharged at the latest.

Due to the high starting currents that MF batteries provide, it is worthwhile to use them despite the high price – compared to the standard type, around 80 euros are due for an average of 80 euros. Where does the better energy yield come from? On the one hand, because the maintenance-free batteries usually have more lead plates in each cell. Michel Urban from the charger manufacturer Tec-Mate illustrates it this way: »Imagine that you cut the thick lead plates of a standard battery into wafer-thin slices like salami. As a result, you can now expose a much larger lead surface to the electrolyte and significantly increase the electrochemical reaction. ”In addition, MF types are provided with higher acid concentrations when they are filled for the first time – this also increases the performance when the starting current is delivered. However, the thin plates are much more fragile and now need better protection. This task is carried out by the glass fiber mats, which not only absorb the electrolyte, but also act as dampers against impacts and vibrations.

Specifying capacity in ampere-hours (Ah) is of little use

The capacity specification in ampere hours (Ah) is of little use with motorcycle batteries. In purely mathematical terms, for example, you can draw four amps of current from a twelve Ah battery for three hours. In relation to the motorcycle, however, this value remains a purely theoretical one. Anyone who sucks a motorcycle battery down to the last drop is doing irreparable damage to it. A capacity specification only makes sense for laptops or mobile phones whose batteries are used cyclically. Specialist author Martin Fischinger (“Motorradelektrik”, Motorbuch Verlag, ISBN 3-613-02405-5) sums it up: “The term is misleading for starter batteries because it suggests that something similar can be done there.”

First and foremost, motorcycle batteries must deliver as high a current as possible when starting. If the engine is running, they go into so-called float mode, in which the alternator charges the battery. In order to be able to effectively assess the performance of the battery, the cold test current would have to be known. How high this is, however, can be elicited from very few manufacturers. There is no obligation to indicate it.


  • The standard type the classic lead-acid battery is very uncomfortable to use. Acid has to be bought separately, filling is cumbersome, and checking is time-consuming. In terms of performance, they go to their knees faster than modern MF types, but cost only half in comparison.
  • The dry cell type Although it is not a classic motorcycle battery, it is becoming increasingly popular due to its very high starting currents. Dry cells can be installed in any position, e.g. upside down. Due to the dimensions that are not always typical of a motorcycle, the battery compartment often has to be adjusted.
  • With the maintenance-free type, Recognized by the abbreviation MF (“maintenance-free”), filling with acid is child’s play thanks to special containers. After the closure has been sealed, checking and refilling is neither possible nor necessary. In the meantime, there are already pre-filled and factory-sealed MF types.


The nominal voltage is discharged with a low current in volts (V)
measured. Twelve-volt motorcycle batteries are six lead-acid cells connected in series. When fully charged, the result is a mathematical value of 12.72 volts, since each cell has a potential difference of 2.12 volts.

The capacity only describes the amount of electricity available from a battery, measured in ampere-hours (Ah). A high one
Ah value is not an indicator of the quality of a starter battery. Much more important is the starting current behavior: That’s right
that, batteries with much smaller capacities can also be used.

The cold test current is a discharge current in amperes (A), which was measured at minus 18 degrees Celsius for a period of ten seconds. The test procedure is regulated in various standards (DIN, EN). Using this value, it is much easier to make a statement about the performance of a motorcycle battery than based on the capacity in Ah. Good specimens deliver 100 to 120 amps.

Right or wrong?


  • …should be generously coated with pole grease before connecting to the terminals. Wrong: pole bold is not conductive. If it is applied to the contact surfaces, the current flow deteriorates. Pole grease offers sensible protection against acid fumes, corrosion or salt spray and should only be applied thinly after the battery has been connected.
  • …can be frozen. Correct: If the batteries are well cared for and charged, the electrolyte only freezes at minus 68 degrees Celsius. Since the self-discharge increases as the temperature rises, a cold place is ideal for wintering.
  • …should always be fully discharged before charging. Wrong: A motorcycle battery does not have a “memory effect”, as is known from laptop or cell phone batteries. On the contrary: Starter batteries are damaged by deep discharge.
  • …can also be shaken. Correct: the start-up process produces water that collects on the plates and then acts like an insulator. This blockage can be lifted by vigorously knocking or shaking it briefly.
  • …are allowed to “cook” while loading. Wrong: Especially with the now very popular fast charging processes, it is important to ensure that the cell temperature remains below 40 degrees Celsius. So-called boiling or gassing puts a lot of pressure on the battery plates, the battery wears out and its service life is reduced.
  • …break faster in short-haul operation. Correct: When starting the battery, lead sulphate is produced, which can crystallize out (sulphation) if the battery is not fully charged (e.g. through frequent short-distance operation). As a result, the battery accepts less and less charging current and becomes increasingly weaker.
  • …can be destroyed by a grain of salt. Correct: If, for example, road salt gets into the cell when the acid level is filled, the self-discharge increases to ten times the value. The cell and thus the entire battery are then broken.
  • …can be checked by measuring the voltage. Wrong: Even empty batteries show twelve to 13 volts during a check. First
    When testing under load (pull out ignition cable, switch on consumer, organ for five to eight seconds), statements are possible. With good batteries the value drops to a maximum of nine, with defective batteries to four to six volts.

Structure of a battery

  • Connection pole: Good conductivity is important. In addition to lead, brass is also used
  • Closing strip: After the initial filling, the cell plugs of this type are permanently sealed
  • Battery cell: Smallest unit of a battery. Your individual components are connected to one another by the cell connector
  • Grid: Basic components of a lead plate (electrode), which are joined together with alternating polarity (positive and negative) to form a plate block
  • Paste: Painted in various mixtures on the positive and negative grids of a battery
  • Separator: Component made of fleece or foil material for physical separation and electrical insulation between the plates of opposite polarity
  • Battery case: Maintenance-free batteries are tightly closed. If the internal pressure is too high, gas can escape through a safety valve

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