How To Charge A Motorcycle Battery

Written by
Matt Finch
Published on
August 27, 2020 10:45:00 AM PDT August 27, 2020 10:45:00 AM PDTth, August 27, 2020 10:45:00 AM PDT

Motobatt Quadflex is a Sealed Factory Activated AGM (absorbed glass matt) battery. For charging, it only needs to have the correct charger with an AGM algorithm applied, making it a very safe and acid free process. While this blog is for Motobatt batteries, the same process is true for any sealed powersport battery.

For other types of batteries which require watering or acid filling, careful commissioning is required to get the most useable life and performance from your battery. It is not widely understood that the most damage a battery may incur is from initial activation stage, since at times the correct commissioning procedure is not followed due to customers being in a hurry and people cutting corners.

This is just one of the reasons Motobatt Quadflex battery is a great choice since the guesswork has been done and the factory have activated the battery to maximize its lifetime potential.

The first part of the battery charging process should always be to check the open circuit charge voltage of the battery. (the battery disconnected and standing by itself) This voltage will give you an indication on the voltage and overall charge rate of the battery. Voltage should be checked as accurate once the battery has been sitting for at least 2 hours after charging or a ride.

As a rule of thumb battery charge rates can be understood as per below:

  • 12.90V = 100%
  • 12.75V = 75%
  • 12.5V = 50%
  • 12.0V = 25%

A battery showing lower voltage than 12.0V may be severely discharged and require a special charger like a Motobatt fully automatic AGM charger.

Maintaining a battery at full state of charge will dramatically increase its life, since each time you load the battery to start the engine, this creates a sudden voltage drop and pulls off charge from the battery which is not immediately replaced. Loading the battery from lower voltages causes the battery voltage to drop even further under load which hurts the battery since you are asking too much from it. To avoid this punitive treatment of the battery, always keep it on a maintainer so it is muscled up ready to go.

Conversely overcharging a battery can be even worse and significantly reduce the batteries life. Drying out the battery by boiling it, and creating too much heat will warp the plates, create shorts and even melt welds inside the battery. To guard against overcharging always use a Powersports specific automatic charger with a dedicated AGM mode, or a Motobatt Powersports charger.

Knowledge Nugget

  • Overcharging usually happens via the following sequence of events in no particular order.
  • Charging for too long
  • Charging at a rate that exceeds the natural absorption rate
  • Using a constant voltage charger with too high a delivery rate or a faulty charging system
  • Charging a battery without the correct electrolyte levels

How do you know what to charge with, and for how long?

The most important thing to know is how many Amps to you use to charge the battery.

Powersports batteries they are very small, and hence they are very sensitive to being overcharged. Do not charge them with a car battery charger!

Batteries have a natural absorption rate which is the maximum rate they can accept a charge without overheating. Imagine drinking from a fire hose, this is overcharging. Microprocessor controlled chargers apply the optimum charge and voltage rates measured hundreds of times per second.

We get calls from people that simply had a flat battery from, lack of use, put it on a constant voltage car charger and “left it on overnight”. Generally somewhere about the 1 hour mark the battery was venting electrolyte like a steam train and slowly turning into a grey sludge. Needless to say, 12 hours later it was “well done” over cooked and irredeemably damaged.

First thing you need to identify what is the Amp hour capacity of your battery. This is indicated in the battery part number. For example. YTX14-BS. The 14 represents the amp hour capacity of the battery as designed by the Original manufacturer. Because there are many cheaper brands using less active material, you may find your battery actually has less Amp hour capacity than the number indicated. In this case for example a cheaper version may only have 12 Amp hours capacity. If you check the manufacturers website or data printed on the battery you will be able to see the actual rated Amp hour capacity. Its s good idea to do this to ensure you don’t miscalculate and overcharge.

Knowledge Nugget

The battery should only be charged at 10% of its rated capacity. Divide the amp hour rating by 10

14 Amp hour battery /10 = 1.4A. So, the battery should be charged at a rate of 1.4 Amps.

For boost charging in emergency you may charge for a short time at no more than 30% of capacity, in this case 4.2 Amps for 30 mins then drop back to 1.4amps. If any heat builds up drop the rate to 10%

When the charging rate of the battery is exceeded heat builds up, like any electrical component heat has a damaging effect. At this point the electrolyte starts to boil and create hydrogen gas. If combined with oxygen these gases are explosive and can be ignited by a spark, so make sure you always turn the charger off before removing charger clips from the battery, and be careful if you have any jewelry that may come in contact with the terminals.

Sealed AGM Battery charging

Follow steps 1-6 at the end of this article.

For sealed AGM batteries they are by design acid starved, so they are more sensitive to being overcharged. Any electrolyte that escapes from the burp valves will decrease the fluid inside the battery, and hence dry the battery out. The electrolyte cannot be replaced so if using a charger that is not automatic you need to carefully monitor the battery at all times. If gassing does occur, let the battery completely cool down, before reapplying a charge.

Charging Times (Est) with 1 Amp Powersport charger

State of charge:

  • 11.5 = 13-20 Hours Required
  • 11.9 = 5-11 Hours Required
  • 12.3 = 3-6 Hours Required
  • 12.7 = 1-2 Hours Required
  • 13 = Charged

The above estimations are based on a standard 1-amp powersports charger. Some people have .5 Amp or 500mA maintainers. These types of chargers are not going to charge a deeply discharged battery. If they do charge, they will be very slow. Generally, a higher voltage charger will be required, and charging time will be longer as the charger goes through the process of de sulphating the battery.

Bottle supplied battery charging (BS)

Bottle supplied batteries are shipped dry charged, sealed to ensure no oxygen or moisture can enter the battery and discharge and ruin the plates. Sealed and kept in a dry location away from heat and sunlight they can last for years. They are sealed by a special foil which is peeled off prior to activation. Once the foil is broken, they should be filled and activated immediately.

These batteries come with a special acid pack which is of a different specific gravity and quality to standard acid. Further it is also an exact measured amount to ensure there are no spills from the battery in normal use, and that there is enough acid to comfortably cover and activate the plates. Do not use an acid pack from a different battery since you may overfill or underfill, or have a different acid quality.

The battery should be out of the vehicle on a flat surface away from any source of heat or flame in a well-ventilated area.

Remove the container of electrolyte from the box and remove it from the plastic storage bag.

Do not pierce or open the foil coating on the container since this will be pierced by the battery when you push it down into the fill points.

Place the electrolyte container filler end down and snug into the filler ports. Once it is nice and level firmly push down evenly across the container to enable the acid to begin to flow into the battery cells.

It may take 10-20 minutes for all the acid to drain into the battery depending on the size, if there are any cells with residual liquid simply tap them to get the balance to drain out. Once empty carefully remove the container and place the filler end into an old rag or paper towel to stop any acid dripping.

Insert the battery filler cap strip, and firmly push down along each cell until its flush with the top of the battery. These are a permanent seal, do not ever remove the strip.

Allow the battery to stand for 2 hours, if you have time overnight is even better. This allows the acid to soak into the paste on the plates and prevent dry charging the battery.

Charging process

Once the settle in period is over the battery will now require an initial charge. At this stage the battery is only around 75% charged, and needs to be charged with an appropriate charger capable of 12.9-14.9v for an AGM battery. Chargers not capable of 14.9V may not fully charge the battery.

  1. Ensure the charger is off, and you have enough space to access the battery.
  2. Place the positive (RED) lead on the positive terminal, then place the Negative (BLACK) lead on the negative terminal. Do not reverse the terminal polarity or you will short circuit the battery an create a spark.
  3. Now check that you have set your charger to the correct amp setting if manual, or if automatic just turn on the charger.
  4. Check the battery in 10 minutes to ensure there are no hissing or boiling sounds, the battery should show signs of slight bubble forming but be cool, and not gassing.
  5. Once your charger indicates the battery is charged, first remove the negative lead, then the positive lead being careful not to touch the leads together.
  6. Now wait around an hour to check the voltage. It should be around 12.85V or higher.

If the battery voltage has dropped below 12.65v, return the battery to the charger for another cycle.