Absorbent Glass Mat (AGM) batteries are commonplace in powersports applications nowadays.

There’s a big reason why: These AGM batteries are virtually maintenance free. Back in the day, a flooded lead acid battery needed to be routinely checked and filled to ensure it could maintain a charge. On the other hand, AGM batteries are pretty much hands off—provided you follow the proper steps to prepare them for the initial charge, that is.

That’s why we’re writing this quick article. If you buy your AGM battery from a walk-in store or dealership, there’s a good chance it’s already been properly charged and is ready to drop into your motorcycle, snow mobile, lawn mower, or whatever.

Many battery manufacturers include everything you need to get your AGM battery ready for its initial charge. For instance, this Yuasa battery came with a single unit of chambered vials (in the bag) filled with the proper amount of electrolyte. (Image/OnAllCylinders)

But if you buy your powersports batteries online, you’ll probably have to set up your AGM battery yourself. And this initial prep and charging process is critical; if you don’t follow the instructions, you risk permanently damaging your battery.

The good news is, these steps are all pretty easy and straightforward.

While your battery will likely come with its own instructions, we wanted to emphasize three tips to ensure your battery has a long service life.

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3 AGM Battery Initial Prep & Charging Tips

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1. Fill Your Battery with the Right Amount of Electrolyte (Not Water!)

For this AGM battery, you remove the heavy rubber plugs from the top of the battery first (do not discard this!), which exposes the pointed fill ports on the battery below. Leave the foil on the electrolyte vials too. (Image/OnAllCylinders)

First off, electrolyte is essentially a fancy word for battery acid. It’s corrosive and can burn the skin, etch surfaces, and dissolve paint—so make sure you take the appropriate precautions when handling and filling your battery, and dispose of excess electrolyte properly.

Next, it’s vitally important to realize that electrolyte isn’t water. Yes, unlike AGM batteries, flooded lead acid batteries get topped-off with distilled water as part of their regular maintenance process, but not before being filled with acid first.

More importantly, don’t confuse traditional lead acid battery maintenance procedures with any of the steps involved with prepping an AGM battery prior to its initial charge. No water, distilled or otherwise, is involved in an AGM battery’s filling process. You need to use electrolyte, AKA battery acid.

When you’re ready to fill the battery, simply invert the vials (with the foil covering still over the vial caps), position them over the individual fill ports, and press down. The foil on the chamber openings will get punctured and battery acid will start filling the battery. Easy peasy. (Image/OnAllCylinders)

In all of our initial battery charging experiences, the AGM battery manufacturer has included the electrolyte with the battery purchase. But if yours didn’t, you can buy your battery acid separately.

Either way, you want to make sure you fill your battery to the proper levels.

This is a traditional flooded lead acid-style battery. But much like its AGM counterparts it needs to be filled with the proper levels of battery acid prior to its initial charge. Then, you can add distilled water as the levels fall later. Note the fill lines near the top of the battery’s case. (Image/OnAllCylinders)

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2. After Filling the Battery, Wait for the Acid to be Fully Absorbed

It should only take a few minutes for the acid to fill the battery, but if it is having problems filling, a few gentle taps with a screwdriver handle will release some bubbles and keep it flowing. Note! Even after the vials are drained, you should still wait to ensure the electrolyte is fully absorbed into the battery. (Image/OnAllCylinders).

This is probably the step that’s overlooked the most. After the electrolyte has drained into the battery…wait! This allows the acid time to absorb into the glass mat. Remember, it’s exactly what the “A” is in AGM, after all.

If you immediately throw the battery on the charger, it could damage the battery and shorten its lifespan. You may not notice it at first but over time, the battery could develop issues like weak starting performance and a rapid discharge rate.

How long you should wait depends on the battery manufacturer, but in our experience it’s about an hour or two. After the wait, you’re now ready to hook it up to a battery charger.

Once the vials are empty, pull them off and replace the rubber plugs that originally came on the battery. Just use moderate hand pressure here—the cap should slide right on flush with the battery surface, sealing it forever. (Image/OnAllCylinders)

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3. Use the Proper Current (Amperage) to Charge Your Battery

Here’s another simple aspect of battery prep that folks can overlook.

If you read our earlier story on EV Battery Life, you already know that batteries don’t always like being charged at high current levels. And that’s especially true for new AGM batteries getting an initial charge. While a lot of battery charger models have selectable current levels in excess of six amps, in our experience, many initial charging instructions call for a lower current rate, more like two amps.

In other words, charging at a greater current rate than specified will not speed up the process!

Many battery charger models allow you to select the charging current. (Image/OnAllCylinders)

Slamming too much amperage into a new battery can fry the acid inside, which again, could significantly reduce its usable life and cause other performance issues. While there’s no universal current rating for every battery, each battery manufacturer will spec the particular battery’s preferred initial charge amperage in the instructions.

In addition to charging current, your battery manufacturer will also indicate how long you should leave the battery on the charger for its initial charge. It’ll usually vary between five to 10 hours, again at a low amp rating.

Hooked up to the charger at low current, our AGM motorcycle battery should be ready to go in a few hours. (Image/OnAllCylinders)

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Follow Your Battery’s Charging Instructions

While these three tips are important, consider them a supplement to your original battery manufacturer’s instructions. You should always read your particular battery’s initial changing and maintenance manual thoroughly before beginning, to ensure you’re hitting all the proper steps.

All told, it’s not difficult to prep and charge an AGM battery for the first time, it’s just critical that you follow all the instructions precisely. Doing so will ensure your battery has a long, happy service life.

Keywords
AGM batteries, battery chargers, battery tech, Yuasa
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Author: Paul Sakalas

Paul is the editor of OnAllCylinders. When he's not writing, you'll probably find him fixing oil leaks in a Jeep CJ-5 or roof leaks in an old Corvette ragtop. Thanks to a penchant for vintage Honda motorcycles, he spends the rest of his time fiddling with carburetors and cleaning chain lube off his left pant leg.