Best Practices To Manage Off Grid Deep Cycle Battery Banks

October 06, 2016

Off Grid Deep Cycle Battery Banks

Love Your Battery.

For those of us who have built off grid systems using batteries as a power storage, we can always agree on one thing. Those deep cycle batteries are really expensive! And sometimes when we need to purchase a whole bunch of them, the price skyrockets and truly scares the hell out of some of us that are looking to become self-sufficient. Power storage is a very important factor when planning to become power independent and we need to take careful steps to manage this very expensive part of our off grid battery system.

The life of a deep cycle battery is directly linked with the amount of power discharge.

Any power storage expert will tell you:  deep discharge and fast recharge seriously reduces your battery life and capacity. The batteries also sulfates faster. Let us first take a look at some data. For example, let’s take a look at a solar deep cell battery is drained to a depth of 70% (30% remaining) and it has a lifespan of 1200 cycles. If we were to take the same battery and discharge it to 50% only, the estimated life cycle increases substantially to 1700. That is a 40% increase in life cycle.

To put it in perspective

  • If a charge cycle is a week, that would add an extra 9.6+ years to the battery life expectancy.
  • If a charge cycle is a day, that would add an extra 1.25 year to the battery life expectancy

Yes, maintaining a good charging cycle is definitely very beneficial to your battery, great management starts with a good calculation of DOD (depth of charge).  The rule of thumb to follow is to make sure no more than 50% of any cycle battery should be discharged. Let’s say your off grid battery bank has a total of 200aH, the cutoff point for discharge would be 100aH. You’re working load should be calculated accordingly with the 100aH charge depth point. The depth of charge should be one of the first initial calculations that should be made when choosing the capacity of your deep cycle off grid battery bank.

There are tools out there that claim to clean, revive and de-sulfate batteries, we have not seen any real positive effect on our battery systems when using these. So instead of spending your money to buy accessories that claim to work, we recommend you invest your budget into getting bigger batteries with more capacity. Building a larger than needed battery bank may cost more, but its also a great investment into a longer lasting battery.

For smaller systems, if you have the money, invest in L-16.

If you are serious with your system, go big with L-16 batteries and avoid using group 24, 27, 31 and most for D and 8D flooded DC 12 volt batteries. These power sources are actually marine batteries and not a real deal deep cycle battery. If your dimensions allow, using 6 volt and 12 volt industrial batteries or off card batteries will get you much further.

For larger off grid systems where a massive amount of amp hours is needed, you can find a cost effective and reliable option in industrial forklift batteries. This lift fork hack is a well know secret among hard-core off grid enthusiast.

Seriously, these forklift industrial batteries are long-lasting, durable and best bang for the buck when you need a lot of amp hours. Whoever thought of using these for large-scale power storage is a genius. Pricing starts at about thousand dollars for 600+ aH, the biggest hurdle when using a forklift industrial battery is the logistics. These bad boys start at half a ton (1000+ lb) is not definitely something for a home DIY project. If you are a 2 or 3 man team, it would be very difficult to move a few tons of batteries without extra help.

If that is out of your budget, get on Craigslist and try to find a used but working forklift battery. You may be able to find something very cheap and useful.

Keep those batteries happy and topped up.

Adding a solar touch to any battery system can go a really long way in longevity. Consistently keeping the power topped up and you may see your battery outperform your expectations. A small solar panel can trickle charge your battery bank and it’s all automatic, there is no management on your end. The best thing of all is that it is a renewable energy and completely free of charge to you. Except for the initial investment of course.

 Monitor your battery and charging data.

To be able to optimize your batteries, you will need real time information and data to help you make the right decisions in optimizing your battery. Whether it’s a thicker gauge wiring, the length of wiring or positioning of renewable energy sources, having hard data will solidify your decisions. For a low-cost and easy to wire power energy meter, we would recommend this LCD display model. We bought this on Amazon and we love it, the price is cheap but the quality and value it delivers makes it truly a great deal. 

Looking ahead.

Lithium based battery systems using LiFePO4 are looking very promising for the future. It is safe to say some time in the upcoming years, lead acid battery system will be obsolete and replace with a form of lithium battery.

There are several reasons why lithium has the advantage

  • Lithium has a extremely impressive charge and discharge cycle, average number hovers around 2000 which is excellent. What makes it even more impressive is that cycle number is with and 80% depth of discharge (DOD)
  • Talking about depth of discharge, a lithium based battery can be depleted up to 80% and still maintain optimal charge and discharge cycle
  • A LiFePO4 battery is much easier to charge, a simple constant current / constant voltage charging method is sufficient and LiFePO4 batteries can also tolerate stronger charging and discharging currents. (This is something that lead acid batteries cannot tolerate without losing longevity)
  • The pricing is getting there: in some countries, LiFePO4 batteries are already at the same price point as lead acid batteries. Making them a viable substitute economically. Using LiFePO4 is definitely an upgrade from the traditional deep cycle lead acid option.

If you are now planning or starting to build your system from scratch, we urge you look into Lithium LiFePO4 for power storage. They require less management and your running costs over the lifespan will reduce because of its improved charging and cycle. Lead based batteries are way higher in maintenance when compared to lithium based batteries. This LiFePO4 battery is one we really like and looks very promising on a large scale power storage facility, check it out on amazon.

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