How Do I Know If My Marine Battery is Gel or AGM?

Gel and AGM batteries need to be charged differently.

Gel and absorbed glass mat (AGM) batteries are commonly used in marine vessels. Both types are considered safer than regular flooded-cell lead-acid batteries that contain sulfuric acid in each cell, which can leak acid if the outer casing gets damaged, or the seas are rough. Gel and AGM batteries won't leak, even if the casing gets badly cracked. An AGM battery can be charged the same way as a regular lead-acid battery can, but a gel battery requires a different charging method. Overcharging can cause the battery to overheat, which may damage the cells. It's important for you to know which type of battery you have.

Instructions

1. Check the label on the side or top of the marine battery to identify if it's a gel or an AGM battery. All batteries clearly state their chemical composition and will have the words Gel or AGM on the label, possibly in more than one place.

2. Check the charging instructions on the battery label, or refer to the instruction leaflet, if one came with your battery. The label or the leaflet will state that a gel battery must be charged using a specifically-designed charger, or one that has variable charge settings. A gel battery must be charged at a lower rate than an AGM battery.

3. Lift up or weigh your marine battery. A gel battery is heavier than an AGM battery, due to its chemical makeup. This may be difficult if you only have one battery so, if you can't read the label on the battery, take it to a battery store and compare the weight of a gel and AGM battery. While you are in the store you can check prices. An AGM battery is less expensive than a gel battery, so if you made a note of the amount you paid for your battery, you can compare the prices of a gel and AGM battery.

References

• Von Wentzel: Battery Types Flooded vs AGM and Gel
• Battery Tutorial: Gel vs AGM Sealed Batteries
• The Inverter Store: AGM vs Gel Batteries