AGM Motorcycle Battery Review

Article by Mark Trotta

In the last three years, I've installed AGM batteries on three different motorcycles with excellent results. They definitely hold a charge better than conventional batteries, even after months of sitting.

What Is An AGM Battery?

AGM is not a brand name. AGM stands for Absorbent Glass Mat, which is an advanced type of lead acid battery. There is a special glass mat separator that 'wicks' the electrolyte solution between the battery plates.

AGM batteries are sealed, spill-free, and maintenance-free. They have a much lower discharge rate than a conventional battery, making them a great choice for vehicles that are not used every day.

Bottle Supplied vs Factory Activated

An AGM battery may be purchased two ways.

Those that are factory activated (electrolyte already added), and those that are bottle-supplied, in which the consumer needs to fill with electrolyte to activate.

Bottle-supplied batteries will have BS at the end of the part number.

Example: YTX16-BS

When bought online, an AGM battery is shipped with a separate plastic bottle of electrolyte. The electrolyte is often referred to as acid, but it's actually a mixture of water and sulfuric acid.

How to Activate AGM Battery

Activating a bottle-supplied AGM Battery is a simple multi-step process, but does require care and patience. Always read the instructions and precautions before you start.

First, place the battery on a flat, level surface.

Removing the foil sealing strip uncovers six angled filler ports.

Adding Electrolyte

Remove the strip of caps from the electrolyte container and place it face-down on the cell filler ports. Hold the container level and push down only hard enough to break the foil seals.

The electrolyte will immediately start to flow into the battery. During this process, you will see air bubbles inside the container. Do not tilt the container while filling.

After about 20 minutes, the electrolyte should fill each cell. The battery requires all the electrolyte from the container for proper operation, so do not remove the container from the battery until it is completely empty.

After filling, the strip of caps is installed, and stays on for the life of the battery.

After the electrolyte was in, I noticed the battery was warm to the touch, and it stayed warm for about an hour afterwards. Before putting it on final charge, I waited for it to cool down. This "stand" period is actually recommended by the manufacturer.

Charging Instructions

After the electrolyte is added, the battery will register about 12.5 volts, but a final charge is still required.

Most all constant-current chargers are capable of reaching the 14.5 voltage that an AGM battery is capable of.

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Best AGM Motorcycle Battery

If you're not familiar with Yuasa, they are the largest American manufacturer and distributor of motorcycle batteries. In 1983, they pioneered the first maintenance-free AGM batteries for motorcycles with the YT series.

The Yuasa YTX20L-BS fits many Harley Big-Twin models 1997 through 2017. It also fits 1997 through 2003 Sportsters.

Dimensions are 6.87" length, 3.43" width, and 6.12" height.

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The Yuasa YT19BL-BS is a direct-fit replacement for many BMW models, including R1150R, R1150GS, R1150GSA and R1200RT models.

It fit perfectly on my old R1100R. The dimensions were exactly the same as the old one (7.4" length, 3.2" width, and 6.7" height).

It even had the OEM-style terminal covers.

Read: BMW R1100R Battery Replacement

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Custom Bike Battery

Because they're not always easy to get to, a maintenance-free AGM battery is a good choice for a custom bike. The battery in the hardtail Sportster below is a Yuasa YTX16-BS. It sits on a metal battery tray underneath the oil tank.

Dimensions of the YTX16-BS are 6" length, 3-7/16" width, and 6-3/8" height.

NOTE: If you're installing an AGM battery on it's side, check with the manufacturer to verify that it can be positioned in that way. Some can but others can't, and it may leak around the terminals.

Shop: Yuasa AGM Motorcycle Battery

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