If you haven’t read my first post on backup battery banks, please do so here. I have discussed the purpose of backup systems and some reasons that a battery bank is a cool solution. Now I will discuss the most important part of the system, the battery.
What kind of batteries do I need to get? Where do I put them? How do I select the proper battery?
First thing to consider is “Do I have a family or children?” It is important here because it will determine the battery choice. If you are going to have the batteries in a location that children will be around them, you may want a safer battery design, but you will be paying for this design. If children are not a concern and lots of power for small price is your choice, then a flooded, lead-acid battery is what you want.
Next, “Where do I put them?” Do you want to place them in your home to make them available during a blackout situation, or would you prefer to place them in an automobile for mobility? My choice for us (at least right now) was a mobile unit. This will allow me to respond to the likely scenario that a tornado will hit my town. I can help others, charge power tool batteries, and run small corded power tools.
All batteries have a power storage capacity, which is usually in Amp-Hours. Recently they have been adding something called Reserve Capacity, which in an attempt to make it simpler for the user, really just made it more complex. We will discuss these quickly. Amp-Hour is the batteries ability to provide 1 amp of current (at battery voltage) for 1 hour. So a 12 volt battery that has a rating of 100AH means that it can provide 1 amp of electrical current for 100 hours, or 100 amps for 1 hour. When using the battery, there is chemical change inside, and the longer time it has to perform, the less damage to the battery. This battery will actually last longer than 100 hours at 1 amp, and will last less than 1 hour at 100 amps, due to chemical change issues. So a long slow draw is better than a short fast draw. For easy math I will use some different values. I have a 10volt battery with 100AH capacity and I use 10 amps. 10volts x 10 amps = 100 watts, and it will last for: 100AH / 10 amps = 10 hours. So this battery will last 10 hours at 100 watts (units for inverters units, which we will discuss later.) I know it is a lot to take in. GET BIG AMP-HOUR NUMBERS.
Reserve capacity is to explain to people that the battery during typical use will last that amount of time. The reserve capacity of a 12volt marine battery is 75 minutes at 25 amps (this will be on the label). They assume that 25 amps is typical current draw. How do we convert this to amp-hours? 25 amps x 75 minutes / 60 (minutes in an hour) = 31.25 AH. So it stinks that they began Reserve Capacity, because now it requires some math from us to find the amp-hour rating. They typical current draw is open to interpretation from each company. Now we know that we want a bigger amp-hour. But this doesn’t tell us the battery type that we want. Basic battery types are:
–Flooded lead acid batteries: These are your typical batteries. Car batteries, Marine batteries, lawn mower batteries, golf cart batteries. There are maintenance free versions and normal versions.
–AGM (absorbed glass mat) batteries (very little liquid and sealed): These are batteries with liquid in them, however considered NON-SPILLABLE. Commonly confused with Gel cell batteries. Can be mounted in pretty much any position, and can be placed in limited ventilation areas.
–Gel cell batteries: Instead of small amount of liquid, these have plates suspended in a Gel. It also has the same advantages as the AGMs. Both the AGM and Gel will cost twice what a good flooded lead acid battery will cost. Advantages because the robustness of these batteries… KIDS. If children will be around these batteries, you could consider these for their intrinsic safety. It would be better than a busted Car battery. I chose two GC2 Golf cart batteries (6 volt) wired in series (+ on one battery to – of other battery) to make 12 volts. These are flooded lead acid, has a very high amp hour rating, is a deep cycle battery, and are made to be jostled around in a drunk-driven golf cart which means that they are very robust for a flooded battery. They have easy access to refill with distilled water when level gets low. These are great for battery banks, but you MUST buy them in pairs (just trust me). If you are looking for a single mobile battery that will be moved around (like through the house from room to room) you can choose a marine battery. They have convenient handles for carrying! They aren’t quite as robust but are a good choice. They are also a deep cycle battery.
“Wait! Twice now you have mentioned ‘deep cycle batteries’. What the heck is that?” Car batteries are made with huge cold cranking amps (self defined) but will only allow to be drained fully 12 or so times before they are trashed. Deep cycle batteries are meant to do this. They can be fully drained upwards of 200 times! Needless to say, we do not intend to drain them, but chances that we will are very high in a backup power scenario. The AGM and Gel Cell batteries are ususally deep cycle as well. It will really be up to you to decide what batteries you will use based on your situation. I chose the GC2s because my battery bank in in my CAR. They are charged by my alternator AND solar panels. I needed them to be robust in my car. I bought Duracell batteries from Sam’s Club.
Good Links: (awesome thing about the Amazon batteries, is that many of them can ship free. Kinda nice for a heavy battery) I am an affiliate of amazon, but not Sam’s Club. This will NEVER change my opinions of products and what you should use.
Sam’s Club Duracell GC2 golf cart battery (the batteries I have)
Optima Gel (one of my recommended for “safe” batteries)
Marine Battery (12 volts)
Remember, If you have any questions or blog subject suggestions, you may email me, comment, or post on my Facebook page.
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