Getting The Longest Life Out Of Your Renewable Energy Battery Bank

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Whether you’re a seasoned pro or if you’re just now starting to explore the idea of transitioning from grid power to alternative energy, you can never have too many reminders about the importance of properly maintaining your battery bank.

When we first went off the grid, we didn’t know anywhere near what we should have known. As a matter of fact we thought we had done a fairly good job of educating ourselves but we soon learned exactly how unprepared we really were.

Our First Costly Mistake

hand full of cashThe first big mistake that we made that ended up costing us a lot of money was when we decided that we would like to add a few more batteries to our little battery bank. When we first purchased our cabin, there was a rudimentary system in place that consisted of four 12 volt deep cycle trolling motor batteries. This really wasn’t meeting our needs so we decided that we would increase the size of the battery bank and pick up a few more batteries. We actually purchased four more of the same type of 12 volt deep cycle batteries to add to our system but we quickly learned that we had made a costly mistake.

Not very long after having added the batteries we learned that our mistake was adding new batteries to an old battery bank. The problem arises when you add new batteries to a bank of old batteries because the old batteries will quickly pull the new batteries down to the state of the old batteries. If the old batteries are in very poor condition, before long you’ll end up with all of your new batteries being damaged and you’ll be left with a larger bank of junk batteries.

We would have been much better off to recycle the old batteries and just install four brand new batteries. So, lesson number one is to never add new batteries to an old battery bank.

Our Second Costly Mistake

After having ruined the new batteries, we decided to upgrade and go with six volt deep cycle golf cart batteries. These batteries have thicker lead plates in them and they are much better suited for renewable energy applications. They cost us a little bit more than the 12 volt marine batteries but we felt like it would be worth the investment.

We were quite pleased with their performance and they served our needs very well for a while until one day when we noticed that they were slowly beginning to hold less and less of a charge. Mistake number two for us was not knowing that it’s very very important to check the electrolyte level in the batteries and add distilled water to batteries when it gets low.

During the process of charging flooded lead acid batteries, the water level in the batteries will slowly go down. If this fluid isn’t replenished with clean distilled water before the lead plates become exposed, subsequent charging will do irreversible damage to your battery bank. As a matter of fact, because we didn’t know about this, we actually ended up ruining our second bank of batteries as well.

Incidentally, you should only top the electrolyte level off when the batteries are fully charged. If you top the low cells off when they are discharged, the fluid will over flow the next time you charge the batteries up and you’ll have a mess on your hands. Make sure you only fill your batteries to the level that the manufacturer recommends.

The Third Lesson We Learned

After having ruined two banks of batteries, we decided to do it right the next time and we invested in some Trojan L-16 deep cycle batteries. If you’re not familiar with these batteries, they are the real deal! They’re a type of commonly used batteries for renewable energy applications and they’re not cheap. They are super heavy duty 6v deep cycle batteries that have the capacity of storing 435 amp hours each. If I remember right, we paid about $300 for each of these batteries and we purchased four of them.

Now, let’s talk about mistake number three that we had to learn the hard way. One of the most important things to remember when wiring a bank of batteries together is to use super heavy gauge wires that have high quality connectors on them.

When we first purchased these new high quality batteries we tried to use some wire that we had laying around the house and some connectors we got from our local hardware store. Using these wimpy wires, it didn’t take long at all before our new batteries stopped performing as well as they did when they were new. Fortunately for us, all that had happened was the undersized wires and the connections ended up corroding and the corrosion at the connection points caused resistance which resulted in the batteries not charging as well as they should.

Lesson number three was to use heavy gauge cables with proper connectors. If I remember right, we went a little bit overboard on this and actually purchased 2 gauge wiring to make sure that there wasn’t any resistance whatsoever in the wires that connected our batteries together.

How To Prevent Corrosion On Battery Terminals

Another good tip that we learned was to apply some kind of protective coating to the battery terminals to prevent corrosion. Corrosion will cause resistance and resistance means that your batteries will be less efficient. I believe we just purchased a can of spray on corrosion preventative from our local automotive store and it seems to be working just fine.

The Effect That Temperature Has On Alternative Energy Batteries

If you do a good job of properly designing the enclosure for your battery bank, your batteries will perform more efficiently and last longer. Allow me to explain; The colder your battery bank gets, the less energy it will be able to store.

Now, before you go crazy and start trying to squeeze every little bit of performance out of your batteries by simply raising their temperature, it’s important to understand that if your batteries become too hot, they will be damaged and their lifespan will be shortened dramatically.

At 32° F (0° C) the capacity of the battery bank will be reduced by as much as 20%. At -22° F (-30° C) the capacity of the battery bank will be reduced by as much as 50%. Have a look at the graph below that shows the the approximate relationship between battery temperature and battery capacity.

Battery Temperature Chart

Relationship of battery temperature to energy storage capacity.

Graph courtesy of

Now that you know how important controlling the temperature of the bank of batteries can be, you might be wondering what you can do to control this variable. One thing that you can do is to install a temperature sensor on your batteries. These devices will actually monitor the temperature of your batteries and adjust the charging voltage accordingly.

In our application, we actually have our bank of batteries installed in an insulated box. During the winter, we have an insulated cover that we constructed that we place over the battery box to keep them warm. This really seems to help keep the batteries from getting too cold which results in both more efficient charging cycles and more energy being able to be stored in our batteries. Note that the box isn’t 100% air tight so any gasses that are produced during charging can escape from the box.

Controlling Charge Cycles Can Help Improve Battery Life

Even under ideal conditions, batteries have a finite number of times that they can be discharged and recharged. This is most commonly referred to as a “charge cycle”. A battery is considered to have gone through a charge cycle when it has been depleted from a full charge down to 20% of its rated capacity (Note: The actual percentage can vary between brands of batteries).

There is a direct relationship between how deeply a bank of batteries is discharged on a daily basis before being recharged and the amount of time that you can expect the battery bank to last. Without complicating things too much, let’s just say that the deeper the batteries are discharged before they are recharged, the shorter their lifespan could be.

You can increase the lifespan of your battery bank in another way and that is to make sure that whatever you use to charge your battery bank on a daily basis is adequately sized to fully recharge your batteries every day. If you don’t have enough solar panels in your system to fully recharge your batteries each day, your batteries will stay in a constant state of partial charge which will result in their lifespan being shortened.

Regularly Equalizing A Battery Bank Could Help Make It Last Longer

bubbles in electrolite

Note: Electrolyte is not actually blue

You should get in the habit of taking the time to equalize your flooded lead acid batteries on a regular basis. When you equalize a bank of batteries, your charger will basically increase the charging voltage by about 10% for a certain length of time. This causes the electrolyte in the battery to start bubbling. This bubbling supposedly causes the electrolyte to be stirred up which should help maintain an evenly concentrated solution.

If this isn’t done, over time, the electrolyte solution at the top of your batteries will become diluted and the solution at the bottom of the batteries will become very concentrated. Be sure and follow the recommendations provided by the manufacturer of your specific batteries to find out what the actual equalization procedures are as well as how often this procedure should be performed on them.

4 Responses to “Getting The Longest Life Out Of Your Renewable Energy Battery Bank”

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  1. Michael Long says:

    I loved your article. Very informative. Continue the good work! 😉

    • Patty says:

      Thanks again Michael. Glad you enjoyed it!

  2. Brian says:

    If you buy another L16 battery bank, you should look into the 2 volt batterys. Very high amp hours.

    • Patty Hahne says:

      Thanks for the tip Brian. I’ll have to look into that when it’s time to replace our existing bank.

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