You will make a lot of mistakes in the beginning of your “off grid” adventures and your batteries will pay the price whether they are deluxe and expensive models or decent quality and cost effective.
If your solar installer/designer tries to sell you a “high end” (and very expensive) battery bank for your first energy system it might be an indication he/she does not have enough experience or is more concerned about profit margins than what is right for you.
It is a shame to spend 10 to 20 thousand dollars (ore more) on a battery bank that will likely not last half the time it was designed for.
Once you destroy your first set (which almost everyone does), you will be ready to invest in a better quality bank.
Here we will discuss the best options when designing a battery bank for someone who has never lived off the power grid before.
Some good choices for the beginner are:
- Trojan T105 Golf Cart 6 Volt 225 AH
- Tojan L16 6 Volt 370 AH
- Surrette S460 6 Volt 350 AH
- Surrette S530 6 Volt 400 AH
TROJAN T105s 225 AMP HOURS AT 6 VOLTS
The T105s are definitely the cheapest but they might not be the best choice for larger systems due to the need to parallel many batteries together to get the required amp hours. What is wrong with paralleling multiple battery strings together?
Trojan’s T105s have a C20 rating of 225 AH (amp hours) at 6 volts. What is a C20 rating?
The usual price for a Trojan T105 is approximately $80-120 USD each. The price is closer to $80 when buying in bulk.
The T105s are a good balance between cost and performance. They were originally made for golf carts but have gained a lot of traction in the solar industry.
Here are the numbers for the Trojan T105 if you were to install one string in your battery bank:
225 amp hours at 12 volts – providing 3.3 kWh at 100% discharge – 2 batteries in total
225 amp hours at 24 volts – providing 6.6 kWh at 100% discharge – 4 batteries in total
225 amp hours at 48 volts – providing 13.2 kWh at 100% discharge – 8 batteries in total
Here are the numbers for the Trojan T105 if you were to install two strings in your battery bank:
550 amp hours at 12 volts – providing 6.6 kWh at 100% discharge – 4 batteries in total
550 amp hours at 24 volts – providing 13.2 kWh at 100% discharge – 8 batteries in total
550 amp hours at 48 volts – providing 26.4 kWh at 100% discharge – 16 batteries in total
A new set of T105s should last 4-6 years if looked after (according to what is taught in this article) in a well designed solar electric system. We have used them for up to 8 years before replacing, although the last few months were not great. If abused and treated poorly, they will last about 1-2 years.
TROJAN L16s 370 AMP HOURS AT 6 VOLT
The better choice for your first bank of batteries is the Trojan L16. They have about 60% more capacity but cost more than double. The reason for the extra cost is they have far more lead and electrolyte than the T105, making them last a lot lot longer.
Trojan’s L16s have a C20 rating of 370 AH (amp hours) at 6 volts. What is a C20 rating?
The usual price for a Trojan L16 is approximately $270-320 USD each. The price is typically closer to $270 when buying in bulk.
The L16 is a great battery for many solar systems as they are well made, have a decent amount of lead and electrolyte and they are a manageable size and weight for transporting. Although we highly recommend them for new off gridders, we also recommend them for experienced solar homesteaders as well. In fact they are what we are using for our main battery bank right now.
Here are the numbers for the Trojan L16 if you were to install one string in your battery bank:
370 amp hours at 12 volts – providing 4.4 kWh at 100% discharge – 2 batteries in total
370 amp hours at 24 volts – providing 8.9 kWh at 100% discharge – 4 batteries in total
370 amp hours at 48 volts – providing 17.8 kWh at 100% discharge – 8 batteries in total
Here are the numbers for the Trojan L16 if you were to install two strings in your battery bank:
740 amp hours at 12 volts – providing 8.9 kWh at 100% discharge – 4 batteries in total
740 amp hours at 24 volts – providing 17.8 kWh at 100% discharge – 8 batteries in total
740 amp hours at 48 volts – providing 35.5 kWh at 100% discharge – 16 batteries in total
A new set of Trojan L16s should last about 6-9 years if well taken care of. We have seen them used up to 12 years and as little as 4 years. Battery care is very important.
SURRETTE S460 350 AMP HOURS AT 6 VOLTS
Another good choice for the solar newbie is the S460 by Surrette. You may have already assumed the S460 would be a 460 AH battery but it is not. It’s C20 AH rating is 350. It’s C100 rating is 460. What’s the difference?
Regardless of the misleading AH rating, the S460 is a well built battery. They are made in Nova Scotia Canada and are usually of the best quality.
The usual price for a Surrette S460 is approximately $300-400 USD each.
They are made specifically for solar electric systems and were originally based on the L16.
Here are the numbers for the Surrette S460 if you were to install one string in your battery bank:
350 amp hours at 12 volts – providing 4.2 kWh at 100% discharge – 2 batteries in total
350 amp hours at 24 volts – providing 8.4 kWh at 100% discharge – 4 batteries in total
350 amp hours at 48 volts – providing 16.8 kWh at 100% discharge – 8 batteries in total
Here are the numbers for the Surrette S460 if you were to install two strings in your battery bank:
700 amp hours at 12 volts – providing 8.4 kWh at 100% discharge – 4 batteries in total
700 amp hours at 24 volts – providing 16.8 kWh at 100% discharge – 8 batteries in total
700 amp hours at 48 volts – providing 33.6 kWh at 100% discharge – 16 batteries in total
SURRETTE S530 400 AMP HOURS AT 6 VOLTS
The Surrette S530 looks exactly like the S460 but it does contain more lead and more capacity. As it is in the exact same container as the S460 the extra lead means less room for electrolyte. Some would argue that adding more lead and less electrolyte could be a problem but it should be mentioned that Surrette actually increased the size of the battery’s case a few years ago when they added a new model…the S600. It even has more lead but right now we are talking about the S530.
The S530 is a well built 400 amp hour 6 volt battery. They are made in Nova Scotia Canada and are a high quality battery.
The usual price for a Surrette S530 is approximately $350-450 USD each.
They are made specifically for solar electric systems and were originally based on the L16. They started with the basic shape and size of an L16 but made it bigger and stronger using thicker lead plates. If you can get a good price when buying the S530, they are a good choice as well for the solar first timer.
Here are the numbers for the Surrette S530 if you were to install one string in your battery bank:
400 amp hours at 12 volts – providing 4.8 kWh at 100% discharge – 2 batteries in total
400 amp hours at 24 volts – providing 9.6 kWh at 100% discharge – 4 batteries in total
400 amp hours at 48 volts – providing 19.2 kWh at 100% discharge – 8 batteries in total
Here are the numbers for the Surrette S530 if you were to install two strings in your battery bank:
800 amp hours at 12 volts – providing 9.6 kWh at 100% discharge – 4 batteries in total
800 amp hours at 24 volts – providing 19.2 kWh at 100% discharge – 8 batteries in total
800 amp hours at 48 volts – providing 38.4 kWh at 100% discharge – 16 batteries in total
- When buying your first set of batteries it can be intimidating to say the least. There are so many choices. Many times the decision will be made for you as you might only be able to get one brand of batteries in your location.
- It is likely that Trojan will be available and cost effective in your area as they are one of the biggest solar battery suppliers on earth. If you really want Surrette S530s but find out that you will have to pay much more for them compared to a Trojan or other brand L16, the non Surrette is the better choice.
- Another consideration is availability and lead times for warranty issues. As nice as Surrette batteries are, they are rarely readily available. When we operated a solar store, it was not uncommon to have a six to nine month lead time when buying directly from Surrette. We were not a small battery dealer either. We regularly bought pallets and pallets of batteries. Prepaying for 6 pallets of S460s and waiting for nine months is very hard way to do business.
If you will have to wait a few months for your battery bank, what will happen if there is a warranty issue?
Are you prepared to wait three to six months to get a replacement for your defective battery?
If not, you better buy what the local battery supplier keeps in stock.
What about other brands of the golf cart battery or L16s?
While Trojan is responsible for putting the golf cart battery and the L16 in the spotlight, there are hundreds of other battery manufactures that make good quality batteries. Some decent names are US Battery, Interstate, Energizer, Deka, Centennial, Universal and Exide. Most golf cart batteries are of reasonable quality. When looking at other brands of golf cart batteries make sure they are in fact 220-230 AH 6 volt batteries and weigh between 60 and 70 pounds. There are lower amp hour golf cart batteries out there that will not provide the capacity you are looking for.
The L16 is a little more complicated to compare. There are many shapes and sizes of L16. They can vary from 200 AH to 400 AH. If you are purchasing some L16s make sure they are in the range of 320 to 400 AH and they weigh approximately 100 to 125 pounds. Most folks don’t realize that even Trojan has many models of L16 that vary from 370 to 435 AH (C20) and weigh between 100 and 125 lbs.
If you can find a golf cart or L16 battery that is made by a known battery manufacturer, and they are readily available and affordable, they are probably a good choice. The importance of having a battery that is readily available cannot be understated. If you have a problem with one or more of your batteries, you will not be able to wait months for a replacement.
Why are you only recommending batteries Flooded Lead Acid (FLA) batteries?
For your first (and probably all) battery banks, flooded lead acid batteries are the best option. Sealed batteries also known as AGM batteries are not very forgiving. Any battery that is sealed cannot be “brought back to life” if you cause any damage by undercharging or overcharging.
With an FLA battery, if you discharge the battery too much and cause a build up of sulfate, you can bring it back to life with an equalization charge. Equalization is a purposely over charging the battery to remove sulfate and mix the electrolyte. However, water will escape and need to be returned. It is easy to add water to an FLA battery but a sealed battery is sealed and cannot take water. If you over charge a sealed battery by mistake (or on purpose), any water that escapes cannot be returned. Learn more about equalization and battery maintenance.
Sealed batteries have their application but they are not usually a good option for the off the grid homestead.
What about used batteries?
This is a request we hear on a daily. Someone knows a guy who can get batteries from a phone or electric company that are being replaced due to regular maintenance. As the story goes, the batteries are like new and just need a new home. This is almost NEVER a good idea.
However these guys seem to know to how to repair old batteries which might be worth looking into?
Phone and electric companies are not stupid. They do not spend money on new batteries because it is fun. They spend money on new batteries as they know the old batteries are worn out. And 99% of the time they are worn out. I hate to see folks spend their hard earned money on junk. Most of the time these companies are thrilled to see you come along with your money and your truck. Discarding batteries is very expensive. You assume that responsibility when you take the used batteries away. Please do not ever buy used batteries. If they are free and you can transport them for free, then it might be OK. Other than that situation, do not waste your time with used batteries.
I can get a whole bunch of 12 volt car batteries for a good price. Will they work?
Absolutely not. Car batteries or starting batteries are not suitable for deep cycle applications. Batteries that are made to start a car engine are made with a lot of very thin plates (to provide a lot of surface area) that provide good surge power, but they will not work as a deep cycle battery. The plates are paper thin.
The average car starting battery is good for about 10 cycles. If you leave your headlights on and drain your battery more than 5 or 10 times, it will be destroyed. The plates will either get hot and warp or be eroded and end up sitting on the bottom of the battery. Deep cycle batteries use much thick plates made to handle deep cycles.
What about 12 volt deep cycle batteries?
Unfortunately, 12 volt “deep cycle”/”marine” batteries do not make sense for the majority of off grid applications. If you imagine a 6 volt golf cart battery, it is composed of 3 – two volt cells that are wired in series to make six volts. There is just enough space to make fairly thick lead plates and fit them in the battery case. Now try and fit 6 – two volt cells in the same size container as in the average “deep cycle” 12 volt battery. There is simply not enough space to do it right.
As a general rule the lower the battery voltage, the better the battery will be for deep cycling. The truth is most 12 volt so called “deep cycle” batteries are not really deep cycle at all. They are really just starting batteries with plates that are a little bit thicker. The term “marine battery” also refers to a starting battery that has plates that are slightly thicker than a starting battery.
The photo below shows the result of deep cycling a 12 volt “marine”/”deep cycle” battery. Note the badly warped plates. They cannot handle the heat generated during hard deep cycling as would be common in most solar homes.
The only time we would recommend 12 volt batteries would be for a tiny system that you do not have to rely on. Maybe you have a cottage and you only want a small system to operate a few LEDs and a radio. In this case a 12 volt deep cycle battery would probably be fine. Another 12 volt battery application would be a solar traffic light or sign light. While a real deep cycle 2, 4, or 6 volt battery would perform much better, an inexpensive 12 volt unit might be OK for small systems.