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Car Batteries 101

Differences between AGM, GEL and FLOODED (wet) batteries

The most common battery for Car, Marine, RV and solar applications is the lead-acid battery, but there are many kinds. First let's look at what makes them similar: Lead acid batteries use an electrolyte that consists of sulphuric acid, and plates made up of lead to chemically store electrons. These batteries consist of cells tied together to provide an adequate amount of electrical energy storage for the need. The lead acid battery stores a relatively large amount of power, for a relatively long time, in a relatively small space. This portable power makes these batteries ideal for these applications.

So what makes these batteries different?

Even though inside all AGM, GEL and flooded batteries contain lead acid, the internal construction of the battery divides them into their respective categories.

Absorbed Glass Matte or "AGM" batteries are the latest and greatest in lead-acid batteries. An AGM battery uses a separator consisting of fiberglass between the plate and wrappers to hold the electrolyte in its place with capillary action. Combining the lead plates, electrolyte, and fiber glass separation fibers in a confined space, AGM batteries create a "physical bond" by way of capillary action. Similar to how water creeps up a towel when it is put in a bathtub. This capillary action holds the liquid inside the glass matting, making the AGM Battery "spill proof" if it is ever exposed. Due to the tight packing of an AGM battery, it is also the most impact resistant, and boasts the least internal resistance. The lower internal resistance increases the output voltage, decreases charging time, and reduces losses to heat as power flows through the system. AGM Batteries then bring the trump card to the table, they are maintenance free. Premium AGM batteries recombine the gases produced internally, back into liquid. This recombination makes the AGM battery maintenance free. No acid leaks, no mess while charging, no corrosion on surrounding parts. You plug in these batteries and walk away. AGM batteries can do anything that flooded and GEL batteries can do, just better.

Flooded or "wet cell" batteries are the most commonly used batteries on the market today. Flooded batteries come in the widest variety of shapes and sizes due to their widespread usage in a multitude of industries and applications. Flooded batteries again use lead plates, a sulphuric acid electrolyte, and plate separators but that is where it stops. Usually flooded batteries are not sealed, and do not recombine the gases to liquids internally. Instead, these gases are vented externally. Internal gases produced are released directly to the environment. Through these same vents can flow acid, steam, and condensation, leading to maintenance. Flooded batteries do require maintenance, in the form of water, to routinely replenish lost electrolyte through the vents. Lead plates start to deteriorate when they touch the atmosphere, so if you fail to maintain your batteries, they will corrode and fail. Flooded batteries hold very good rates of charge for the price, but require more work. Unfortunately due to the internal construction, flooded batteries have the weakest internal construction, and some very high internal resistance statistics.

GEL cell batteries are also sealed just like the AGM battery listed above. That is where the similarities end. A GEL battery uses a silica (sand) to turn the sulphuric acid into a jelly like substance. This jelly is then used as the electrolyte. Great care must be taken with GEL batteries not to expose them to high amperage situations. High amperage situations can literally 'SCAR' the jelly inside of a GEL battery, creating a pocket. These pockets allow the plates to begin corroding, leading to premature failure. GEL batteries should not be used for fast charging/discharging, or high amperage charging/discharging situations. Use the other types listed above for these high amperage situations.

GEL Batteries are slightly stronger in regards to internal construction than a flooded battery, but pale in comparison to the physical strength of an AGM battery.

The Difference between Starting & Deep Cycle Batteries

Generally, battery manufacturers produce two different types of batteries. One is designed to give all it's available power in 20 seconds (starting batteries), the other is designed to give it's power out over time measured in minutes or hours (deep cycle batteries). The fundamental differences are built in during the manufacturing process, so no amount of care can make a starting battery perform as a deep cycle battery, you just have to buy the right one. Therefore, please select the proper type of battery for your application, or expect it not to work so well or for too long. Below we have taken a few paragraphs to explain the point and proper application for each battery type.

Starting Batteries

Starting batteries, those designed to give their power in 20 seconds or less, are designed to start motors. The starter motor on an engine needs this amount of power to start, and then the engine makes enough power to replace it with either an alternator, generator, or similar device. These batteries are not designed for prolonged electrical usage, like lighting the baseball diamond, or running the car stereo while you work and the truck is off. These types of activities will inevitably lead to a shortened life on your battery.

Starting batteries are built with thin lead plates inside the battery. These thin plates afford maximum amount of surface area for the chemical reaction inside the battery. The ample surface area allows the chemical reaction necessary to generate the electricity inside the battery to happen very rapidly. However, these thin plates are not as resilient to the acid, and break down more quickly when they are fully discharged. This erosion of the plates is accelerated by deep or prolonged discharging.

Deep Cycle Batteries

Deep cycle batteries are designed to give power out over time measured in minutes, hours, or days. These batteries are designed to run electronics, or systems over time. The telecom industry uses them to keep the cell phone towers running. Your boat needs this power for radar, communications, and navigation. You like having the power to run the kitchen as well, stove, refrigerator, and microwave. There is not an electrical circuit that can not be powered by deep cycle batteries when you have inverter too. When you want power, you pull it from a deep cycle battery, push it directly to the load or through an inverter to make AC power. Install the proper plugs, and you can run the appliances from home.

Deep Cycle batteries are built with very thick lead plates inside the battery. These thick plates are able to sustain the acid without breaking down for a longer period of time. The thicker plates are designed to be in the chemical reaction that produces the electricity for a longer period before the plates erode into the acid. This longer period allows you the customer to run electronics for long periods of time, recharge the battery, and see very little capacity lost.

Battery Charging 101

Charging a battery is like filling a water tank, how long depends greatly on the size of the hose. Fill the tank with the garden hose, your going to be there a while, and may not have the right stuff for the job. Fill the tank with the fire department's equipment, and you'll be done in a few minutes, they always have the right tools. Same thing goes for battery chargers, there is a right tool for the job, and size matters.

The right tool for the job is important, no matter what you do. With a battery the same applies. There are predominantly 3 types of battery chargers:

1. One stage battery chargers - aka no brains, hook battery directly to generator
2. Two stage battery chargers - electrical computer brains to monitor charge cycle.
3. Three stage battery chargers - higher tech computer brains to monitor things.

Long story short, if you aren't as attentive for 24 hours as the computer will be, buy the better charger. A two or three stage charger is mandatory if you don't want to harm those batteries. Remember that your batteries weren't cheap, and you are now protecting that investment. A computer chip is basically your insurance.

Long story short, both 2 and 3 stage chargers flip through a series of stage, cycles, or modes as they charge the battery. Each mode has pros and cons, and so by using a symphony of these modes, you get the best results. Bulk mode fills the battery as fast as the sticker on the side of the charger allows, until it gets about 80% full. The bigger the charger, the faster float mode runs up to 80% full. Next a charger flips to float or absorption. Absorption finishes the battery quickly at higher voltages. Float finishes the battery slowly (24-96 hours), and compensates for sulfation in a prolonged storage scenario. For a complete explanation of battery charging modes click here.

Batteries and the stuff inside of them are not inherently stable. The electrons they contain are desperately trying to move. As those electrons are held in check by the chemicals in the battery, a bit of power is lost, perpetually. We call this loss self discharge, or the self discharge rate for a battery. Trickle chargers compensate for this phenomenon.

Trickle Chargers, Float Chargers, Self Discharge Rates and How it Works Together

Batteries are not inherently stable, they are holding onto power, electrons, that desperately want to move. As they are held in check, a bit of power is lost, perpetually. We call this loss self discharge, or the self discharge rate for a battery. Generally a battery starts to self discharge in the first seconds it is removed from the charger.

In the first 24 hours the battery will lose between 2% (Premium AGM batteries) and 10% of it's original charge. Again this process will repeat itself over the next 30 days to leave an AGM battery at 90% (100% - 5% day 1 - 5% over 30 days = 90%) full. For a flooded battery one should expect to return to an 70% charged battery in 30 days due to self discharge, (100% - 15% day 1 - 15% over 30 days = 70%). The moral of the story, if you want to leave a battery unattended, you need to replace that lost current, or your well will run dry all by itself.

Some like the water tank analogy; your battery is a power tank, like a water tank, but it has a leak. If you don't charge it with a small trickle, the hole in the bottom will drain your tank.

Trickle chargers are designed to compensate for the self discharge loss involved with the sustained storage of lead acid batteries.

When using large banks of batteries and installed chargers, the trickle function is usually inherent, but referred to as the float cycle.

A float cycle is a charge at the same voltage as the full battery. If the battery is full at 13.1 volts, 13.2 or 13.1 volts would be the proper trickle charge for the longest life.

Should you want to keep the batteries a little fresher (more charged), but not as long (months between replacements), you tune that trickle or float voltage up a bit to say 13.5 volts.

Battery Charger Warnings

Always read and follow the manufacturer's battery charging instructions prior to connecting your battery, or trying to charge a battery bank. Do not attempt to charge batteries in a confined environment. Explosive and hazardous gases are an inherent byproduct of battery charging, do think ahead. Batteries contain sulphuric acid, and lead, both of which are hazardous material if removed from the battery, or disposed of improperly, do take care to be environmentally responsible. Batteries are useful, just be safe.

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