How to maximize the lifespan of your AGM deep cycle battery

This is by far the most common question that we get asked by boat owners, electric scooter enthusiast, and electric wheel chair owners. Deep cycle batteries come in several different group sizes, terminal configurations, and chemistry depending on the application that they are used for. We specialize in 12V AGM deep cycle batteries so I will be referencing this throughout the guide however this article will still apply to flooded conventional style as well.

Cycle Life: Don’t run your batteries into the ground every time

All deep cycle batteries regardless of chemistry will have a set amount of charge cycles in which it is rated to perform at its optimum level. If you take a look at figure 1 below you will see the cycle life performance and expectancy for our EVH12390 - a 12V 39AH U1 battery.

The first thing that you will notice is that there are three separate possible cycle lifespans shown on the graph each with a different depth of discharge. For a deep cycle battery the depth of discharge will be how much of the reserve capacity has been spent or taken from the battery. So the first line on the graph going from left to right reflects a 100% discharge of the battery every single cycle. In other words the deep cycle battery is run all the way down and charged all the way up for every cycle until it reaches the end of life expectancy at the 300 cycle mark.

We always recommend to all of our customers looking to maximize their battery lifespan to not run their batteries all the way down every time if it can be helped. The less capacity used in the battery prior to charging back up will greatly improve the cycle life of the battery which is depicted in Figure 1 by the second and third lines.

Proper Charging and Storage Practices

The number one reason for early deep cycle battery failure is sulfation. Sulfation occurs when the battery is left in a discharged state for a brief (one week) to a long (several months) period of time. Essentially what happens is that when the battery is being drained the lead sulfate converts to a stable crystalline which then deposits on the negative plates of the battery. This process is reversed when the battery goes into a charge cycle. The longer the battery sits in a discharged state with these crystalline deposits, the harder they become on the plate which in turn makes them more difficult to remove.

The solution to prevent sulfation from occurring is to keep your deep cycle battery in a charged state. That means charging your deep cycle battery after every use. If you have an application that is stored during the winter months - i.e. boats and electric scooters - then ideally you would have an automatic battery maintainer to keep them topped off until the next season. If you do not have a battery maintainer then it is recommended to pull the batteries out of storage once every two months and place them on charge. Deep cycle batteries are capable of retaining a charge for roughly three months of inactivity, putting them on charge every two months will ensure that sulfation does not have an opportunity to set in.