AGM Motorcycle Battery Review
Article by Mark Trotta
I've installed AGM batteries on two of my previous bikes with good results. They 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.
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.
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 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.
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.
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 older chargers do not have enough charging voltage to top off an AGM battery completely. Old trickle chargers may only charge up to 13.5 volts.
Most all constant-current chargers are capable of reaching the 14.5/14.7 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 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.
Read: BMW R1100R Battery Replacement
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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.
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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 on a metal battery tray underneath the oil tank.
Dimensions of the Yuasa YTX16-BS are 6" length, 3-7/16" width, and 6-3/8" height.
Shop: Yuasa YTX16-BS Battery
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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