Maximizing the Durability of Deep Cycle Batteries

As solar storage and electric vehicles become mainstream, careful management of batteries can make or break them.

I learned a couple of years ago that the proper way to us a battery is not to simply charge it up, drain it down to nothing, and charge it up again. My learning curve occurred because I had just purchased an electric trolling motor for a small boat. I had two heavy-duty 12-volt gel-type batteries on board, and hoped to travel 6 miles one way for a there-and-back-again day trip.


Charge Wisely Even the best heavy-duty deep cycle batteries need careful management if you want to extend their lifespan to its maximum. 

At about the end of the first leg, however, both batteries had dropped to about 20 percent power, and I had to do some hard rowing to get back to my starting point.

To make matters worse, my batteries were never quite the same. No matter how long I put them on the charger, they didn't achieve more than 80 percent of their former glory.

So I asked around, and did some research. What I learned is that, depending on the type of battery, deep discharge is a bad idea.

I think what's happened is that we've become used to thinking about the Lithium Ion batteries in our cellphones. We charge them frequently, often draining the phone completely before doing so, without noticing any severe effects on charging ability. But these small batteries have very different characteristics than a deep-cycle lead acid battery of the type used in most solar storage systems.

Deep cycle batteries, can handle more significant rise and fall of charge, but that's true only to a point (typically down to about 20 percent of capacity). A battery allowed to drop too low--to 12.1 volts or lower--now has its lifespan drastically reduced.

According to the Deep Cycle Battery Store, "a deep discharged battery is good for only so many cycles (from as low as 20 in an automotive battery to 180 in a golf cart battery, with the typical RV/marine battery good for no more than 30)."

I'm sure most of us want and expect more than 30 charging cycles from any battery.

The best way to make that happen is to monitor battery health, and never allow the battery to "deep discharge." The chart below can help you in estimating the state of charge of your batteries.

Temperature has some bearing on battery life and performance as well. Batteries generally perform better in higher temperatures, but they also lose their charge more rapidly in storage, if stored in a hot place. The second priority for extending the life of deep cycle batteries, then, is proper storage.

Recommended Storage Practices

Along with how a battery is used, other variables greatly impact battery life. Trojan Batteries offers the following tips on keeping batteries viable and extending power output:

  1. Batteries should be stored in a cool, dry location, protected from the elements. Wind chill factors have been known to freeze batteries which would not freeze at normal ambient temperatures. Direct exposure to heat sources, such as radiators or space heaters, will accelerate the rate of self-discharge and increase the frequency of required boost charging. Exposure to direct sunlight may result in fading of colored cases and covers.
  2. According to Battery Council International, batteries in storage should be given a boost or freshening charge when the specific gravity value drops .040 points. When hydrometer readings are not accessible, open circuit voltage readings may be used. While in storage, a freshening charge should be given when the battery voltage drops below 12.4 volts for a 12 volt battery, or 6.2 volts for a 6 volt battery. Table 2 shows open circuit voltage values at various states of charge and recommended recharge times at various charge current rates.
  3. If the batteries have been in service prior to storage, they should be given a boost charge before being placed in storage and immediately prior to returning to service. Proper storage of Trojan deep-cycle, lead-acid batteries will help achieve better performance and longer life, while increasing reliability and value to the end user.

battery state of charge reference chart Source: