Classic Motorcycle Build

AGM Motorcycle Battery Review

Article by Mark Trotta

Recently I installed a Yuasa AGM battery in my old Beemer. I had previously installed the same type on a Harley Sportster and had good results. They hold a charge better than conventional batteries, even after months of sitting.

AGM battery for motorcycle

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.

Factory Activated vs Bottle Supplied

There are two types of AGM batteries. 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.

Yuasa AGM battery review

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 an AGM Battery

Activating a bottle-supplied AGM Battery is a simple multi-step process, but does require care and patience. First, place the battery on a level surface. Removing the tin-foil strip from the battery uncovers six angled filler ports.

Adding the Electrolyte

Place the electrolyte container face-down into the cell filler ports. Hold the container level and push down only hard enough to break the foil seals.

how to activate an AGM battery

The electrolyte will 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 will 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.

Yuasa AGM battery review

After filling, the plug strip is installed. The plug strip 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 the battery casing to cool down. This "stand" period is actually recommended by the manufacturer.

AGM Battery Charging Instructions

With the electrolyte added, the battery registered 12.5 volts on my digital multimeter. However, a final charge is still required.

Most all constant-current chargers are capable of reaching the 14.5-14.7 voltage that an AGM battery is capable of.

motorcycle battery tender

Most older chargers do not have enough charging voltage to top off an AGM battery completely. For instance, my 10-year-old trickle charger only charges up to 13.5 volts.

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Best AGM Motorcycle Battery

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

The battery I installed in my BMW R1100R is a Yuasa YT19BL-BS. The dimensions were exactly the same as the old battery (7.4" length, 3.2" width, and 6.7" height). It even has OEM-style terminal covers.

Yuasa AGM battery review

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The Yuasa YTX20L-BS fits many Harley Big-Twin models 1997 through 2017. It also fits 1997-2003 Sportsters. Dimensions are 6.87" length, 3.43" width, and 6.12" height.

Yuasa YTX20LBS AGM battery review

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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 inside a metal battery box underneath the oil tank.

AGM motorcycle battery review

Dimensions of the Yuasa 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.

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AGM battery for motorcycle

Shop: Yuasa AGM Motorcycle Battery