How to: Look after your motorbike’s battery

A little maintenance will help your motorcycle battery last and keep its charge

Charging a motorcycle battery on a work bench

by Jim Blackstock |

Keeping your bike’s battery in tip-top shape is a key element to ensuring you can enjoy your riding as much as possible. There is nothing worse than excitedly approaching your bike only to find the starter won’t spin over (even though the kill switch is on and it’s in neutral) because the battery is flat.

There are several types of batteries. The most common is (or was) the lead-acid wet-cell type which in past times was accessible though now is less common. This type featured lead plates suspended in a solution of acid and distilled water and each cell (there were six in 12V batteries and three in 6V ones) could have its water topped up to maintain a certain level.

Lead-acid wet-cell batteries have eventually phased out. They were replaced by sealed, maintenance-free batteries where the acid is held in glass fibre matting. Any gasses produced by the chemical reaction generating the electricity were re-absorbed into the liquid, so they didn't require any topping up.

Ring RSC706 Smart Battery Charger

Gel batteries work on a similar principle but instead of familiar liquid, the acid is more of a gel-like consistency and these kinds of batteries can be mounted on their side instead of standing upright.

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Finally, the increasingly common lithium battery, with the numerous scare stories that accompany them.

However, these are largely unfounded: these batteries produce the same electrical power but more efficiently. They are lighter than other options, but also require slightly different maintenance charging regimes.

Generally speaking, a 12V motorcycle battery will have six separate cells joined electrically, each generating 2V. A fully-charged battery in its resting state should show a voltage of around 12.8V, dropping to one that is around 1/4 charged showing 11.7V and a totally discharged battery showing around 10.5V. If yours shows less than that, it is certainly time for a recharge and possibly, a new battery.

With the engine running, the voltage across the battery terminals should be in the region of 14.4V – any supply voltage higher than around 12.5 will recharge the battery. However, it’s worth remembering that many modern bikes will have a slight parasitic drain on the battery when they are stood – ECUs will require some power, however minor, to maintain a memory function and a tracker, if fitted, can drain a battery in a few days or weeks.

Fitting a charger to your bike to maintain the battery is always a good idea, whether you leave it for a couple of days (over the weekend say) or lay it up for winter. Don’t forget that electricity is generated by a chemical reaction within the battery and lower temperatures always slow this process.

A charger that has a maintenance function will vary the charging cycles to prevent long-term damage as well as automatically detect the type of battery and adopt the right charging strategy for it (lead-acid, lithium etc).

Here's how to check your battery and make sure it is top tip.

Step 1:

A motorcycle battery in situ on a bike
©Photo: Bauer Media

The first thing to do is locate your battery. Generally, it will be under the rider’s seat, so check in your handbook how to remove the seat and do so. It should be obvious where it is, but if you can’t immediately see it, look around. Sometimes they are hidden behind panels, or even below the fuel tank and can be tricky to get to.

Step 2:

A motorcycle battery
©Photo: Bauer Media

Once you have found the battery, check what sort it is. Most modern bikes will probably come with a maintenance-free AGM type battery, so assuming there is nothing wrong with it, there is very little you can actually do with it.

Step 3:

Older-style motorcycle battery
©Photo: Bauer Media

If you have an older classic bike, you may still have a lead-acid wet-cell battery, so you will need to periodically check the level of acid in the cells. Here you can see that the levels are very low – this battery is almost certainly beyond saving and will need to be replaced with a modern solution. If the levels were slightly lower than the ‘Lower Level’ line, then you could top each of the six cells up with distilled water to a level between the two lines but if they are this low, it’s a goner.

Step 4:

Testing a motorcycle battery with a multimeter
©Photo: Bauer Media

Depending on how your battery has been performing, you may want to check its condition with a multimeter. If it has been a bit lazy, select the Direct Current range that will show around 20 Volts maximum and check across the terminals with the probes; red to positive and black to negative. You should be looking for between 10.5 and 12.5 volts or so. As you can see here, this one is quite discharged and possibly on its way out.

Step 5:

Connecting a battery charger
©Photo: Bauer Media

Many chargers can detect a discharged battery and help revive it. This one from CTEK does and also has a range of maintenance features to help bring a poorly battery back to decent health, including helping to remove the build-up of sulphur on the surface of the cell plates, which can have an insulating effect. During charging, you should expect to see 14V or so across the battery.

Step 6:

Revived motorcycle battery showing correct voltage reading
©Photo: Bauer Media

A fully-charged motorcycle battery should show in the region of 12.5-12.8 volts in its resting state. This one has been revived, but during periods of inactivity, would be left connected to the charger to maintain the battery and keep its charge topped up.

Step 7:

Adapter to allow easy connection of a trickle charger
©Photo: Bauer Media

Most chargers will come with a pair of crocodile clips but also, a harness to connect and fit the bike so that it can be connected using quick-release connectors. These make it super-easy to pop the bike on charge as soon as you park it. When in the garage this is perfect but some, like the CTEK, are weatherproof and can be used outside if you don’t have access to a garage.

Step 8:

This reading indicates that the battery is charging while the bike is running
©Photo: Bauer Media

While you have the multimeter out, it’s worth checking the bike’s charging system to make sure that it is up to spec. Again, the battery’s resting state should ideally show around 12.5 Volts but with the engine running, the multimeter should indicate roughly 14.4V across the battery’s terminals, indicating it is being charged. Much more or less would indicate a problem of some kind.

Step 9:

A solar charger can be an option to keep your bike's battery topped up
©Photo: Bauer Media

If your bike lives outdoors and you don’t have access to mains electricity to connect to a charger, then there are several solar options available, such as this one from Optimate. These can be left on display and come with a charge controller so that they maintain the battery’s charge and don’t overcharge it irrespective of how long they are connected for.

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