I’ve been looking at batteries and it is crazy all the options there are with 12-volt lead batteries.
I found 3 types of 12vdc batteries available and each does certain things better than the others.
Batteries comes in three basic types.
1) Car battery for fast high current; not good for long slow drain on it.
2) Marine deep cycle battery; Made for high current (MCC; marine cold crank amps) but the lead plates
are bigger and will work better than a car battery for slow current draws.
3) Deep Cycle batteries; these are designed with larger lead plates and work well with slow drain on it.
These batteries are not so good for fast high current like a car battery.
Deep cycle batteries are what you need if you are using wind or solar to power you home.
4) Lithium ion 12 volt DC batteries are available but the price is very high.
Then you have;
Wet Cell or Flooded; batteries like you will find in your car.
AGM Absorbed Glass Matt; The electrolyte (acid) is suspended in a gel solution.
This battery is better for deep cycle use and charges better.
Most of these batteries are sealed and you can uses them inside your RV.
Gel; It is like the AGM.
Then you have different labels on the batteries.
CCA; Cold Crank Amps
MCCA: Marine Cold Crank Amps
Ah; Amp hours,
RC; Reserve Capacity. This is the minutes a charged battery will drive a 25 amps load until the battery
drops below 10.5 volts.
Now you have to figure out if you are going to use 6 VDC batteries in series or 12VDC batteries in parallel! I have heard that the 6VDC batteries used in golf carts are better for power off the grid. I think they might be but for now I am using regular 12VDC deep cycle batteries.
How to calculate parallel and series batteries.
If you plan to use two 6 V DC batteries in series for your 12 Volt source
you double the voltage not the amps.
If you want more amps you must parallel your batteries.
Two 100ah 12VDC batteries in parallel will give you 12VDC and 200ah,
you add up the amp hours the voltage is still 12 volts.
The first thing to consider is how much power (amps) you’ll need to run the things you want to power up.
Example; 19” TV uses 1.3 amps/hour 2.6 cuft refrigerator uses 4.5amps/hour That would be about 5.8amps/hour.
If you know the amps you need each hour then you can divide it into the battery amps and figure out roughly how long you can go before the battery dies. Example; 100ah battery drawing 5amps/hour equals 20 hours of operating time. This is not exactly true but it gets close to the time. You also must consider the duty time of the devices you are running. Also, the inefficiency of the inverter. Fore instants the refrigerator draws 4.5amp while it is running but it only runs about half the time. Plus, inverters use up about 10% of the power, so you have to add that in. The last thing you need to consider is the battery should never go down below 10.8 volts. If you draw the battery down below this the battery won’t last as long as you want it to. The plates start to get clogged up and the battery loses power faster.
Car and Marine batteries are labeled with the cold crank amps available to you.
Deep cycle batteries are labeled with amp hours; 100ah
Some marine batteries will also have the amp hours listed. My Everstart marine battery says 114ah.
Another thing to think about is charging the batteries. You need to put more power into the battery than you want to get out of the battery. This is because the battery itself isn’t very efficient. I’ve read that you need to put about 20% more power in than you get out. So, if you use 10amp hours you’ll need to put about 12amp hours back in just to get back to the 10 you used.
Now if you are using solar panels to charge the batteries plan all this current stuff so you don’t come up short.
Another thing to think about is the charging of the batteries. Solar panel charge controllers are good because it controls how much current is getting to the battery as it charges. You don’t want to over charge the battery because that will shorten the life of the battery. A good charger changes the charging pulses to the battery as it gets closer to 100% charged. If the battery is depleted to will send lots of current to the battery, as the battery gets closer to full it slows down the amount of current. This is the best way to charge a lead battery.
Last thing is don’t let your lead batteries sit without a float charger on it.
A battery that is not being used and recharge will have a short life.
Some Information Sources;