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WTF Is the Deal With Batteries Tutorial

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  • WTF Is the Deal With Batteries Tutorial

    OK so it is catch title but a question I answer every day. So here is a canned answer.

    For Renewable Energy (RE) applications lead acid batteries (Pb) offer the most practical and economical solutions. Other chemistries like NiCd, NiMh, NiFe, and Lithium family are just not economical today.. Lithium is getting close, but that is another story.

    There are two classes of Pb battery family of Wet (aka Flooded) and Sealed Valve Regulated Lead Acid or VRLA. Flooded aka FLA offers the best economics with good performance. There are 3 primary operational groups of batteries; Starting-Lighting-Ignition (SLI), Hybrid deep cycle (aka Marine, Golf Cart, RV, etc.), and true Deep Cycle. Of the 3 types, only 2 are of any interest to RE applications being Hybrid and Deep Cycle.

    * SLI Batteries are just what they imply. A battery that is designed to crank or start an engine (high amps) and be recharged quickly. They are constructed with multiple thin spongy plates made of Calcium alloy to provide maximum surface area which lowers the internal resistance as low as possible. Low resistance means it can deliver very high short burst of current with minimum voltage sag or voltage drop. The plates do not go to the bottom of the Jar to allow room for plate flaking and corrosion build up. SLI batteries become resistant to recharging when deeply discharged.

    That is great for starting engines. Exactly what your vehicle needs, but that does not work well for RE applications. If you try to deep cycle them, those thin spongy plates dissolve and end up in the bottom of the battery jar in 200 cycles or less. DO NOT USE SLI batteries for RE applications except in an emergency.

    SLI batteries are easy to spot in the Specifications. They will only have CCA, CA, and HCA, MCA ratings. Some will even have RC Reserve Capacity Minutes @ 25 amps. You will not see an AH rating. Enough said as you should get the point.

    * True Deep Cycle Batteries are exactly opposite, and generally the best choice for everyday use in RE applications. They are the exact opposite of SLI batteries. They have fewer but very thick heavy plates made made of Lead Antimony that allow them to last much longer and deep cycle. Depending on Brand and Quality up to 5 to 8 years if not cycled below 50% in a day. The trade-off is they have higher internal resistance which limits discharge and recharge current rates. If you discharge them to fast of C-Rate, they will have excessive voltage sag or voltage drop. Voltage drop will cause Inverters to trip off-line form Low Voltage on a fully charged battery.

    As a Rule of Thumb you want to limit the maximum charge/ discharge rates of Deep Cycle Flooded Lead Acid (FLA) to C/8-Hour rate. Where C = the Amp Hour (AH) specification of the battery at the 20 hour rate, and the number is the Hour Discharge Rate. For example a 100 AH battery C/8 = 100 AH / 8 H = 12.5 amps. So if that battery is 12 volts @ 100 AH it can handle a maximum Inverter and charger of roughly 12 volts x 12.5 amps = 150 watts. The minimum charge rate for FLA batteries is C/12-Hours to prevent stratification of the electrolyte. Stratification means the heavier acid well settle to the bottom and float the lighter water on top. A minimum C/12 charge rate will cause slight rolling and gassing of the electrolyte and stir it up.

    True Deep Cycle batteries are easy to spot in the Specifications. They will only have AH and sometimes RC. They will never have any Cranking Amps (CCA, CA, HCA, or MCA) in their specifications. Note you can try to crank with them in a pinch. but do not expect to much as their Internal Resistance is higher and is going to greatly reduce Cranking Amps. But if you know what you are doing you can charge your dead RV or Boat cranking battery with them to ge tout of a jam. In fact some Isolators have that feature built in them, but I did not tell you that.

    * Hybrid Batteries are useful in RE applications. Like the name implies they are a cross between SLI and True Deep Cycle batteries trying to be both. To do this two trick pony, the negative polarity plates are made from Lead Calcium Alloy, and the positive plates are made from Lead Antimony alloy. They also have fewer thicker plates than SLI batteries to obtain some deep cycle capability, and lower internal resistance than Deep Cycle for decent high current charge/discharge rates. However the plate s are not as thick and heavy as True Deep Cycle batteries, thus will not give you the cycle life of a Deep Cycle battery. . So what you get is trade-offs.

    They can deliver/take higher discharge/charge currents than True Deep Cycle, but not as much as SLI batteries. On the other hand they do not have the high number of cycles as True Deep Cycle batteries. Again a trade-off. For the FLA types you still have the lower limit charge rates of C/12 to prevent stratification, but on the charge/discharge side of FLA hybrids you can go as high as C/4, and some cases C/2. This makes them very useful for folks who use over sized Inverters or have to use high charge rates because of low Sun Hours in winter. So they have some good applications in cycle service, but you have to sacrifice charge cycles to get it.

    You can spot a hybrid battery instantly in the specs and Market Names for them. In the specs they will list AH, RC, CCA, CA, and NCA trying to be all things. They come with all sorts of names like Golf Cart, Floor Machine, Trolling, EV, RV, Marine, Liesure, RV Deep Cycle, Marine Deep Cycle, Leisure Deep Cycle, and to whom do I have to give oral gratification to get some service around here.

    VRLA aka Sealed Lead Acid or SLA

    Valve Regulated batteries are the other class of lead acid batteries. The come in two types. of AGM (Absorbed Glass Mat) and Gel.

    *Gel batteries should not be used. End of story. They are made to be charged slowly at C/20 or less, and operate at slightly lower voltages. The electrolyte is gelled and if charge too quickly or even slightly over charged dries out the gel leaving cracks and voids in the electrolyte. Think of that Christmas Jello mold you found in the back of the fridge sitting uncovered in April. They are great for Float Service Emergency Stand By using slow charge Float Chargers like those found in Emergency Egress Lighting and Alarm Systems. Enough about Gel batteries. DO NOT USE THEM

    AGM's are hybrids and are extremely expensive. However they do have applications in RE systems. AGM's have extremely low Internal Resistances, lowest of the Lead Acid family. You see them used in a lot in UPS systems, Golf Carts, Floor Machines, and Electric Vehicles where very high discharge and charge rates are used. In RE applications they are useful when you must charge at very high rates, or extremely large Inverters for a small battery. Rates can go as high as C/2 and in some UPS packages 4C or 15 minutes. Having said that for this discussion, C/4 is about as hard as you want to push them.

    They have additional uses in RE applications like extreme cold, mobile, or unusual mounting orientation like on their sides. They were invented for military and aerospace industry. The downside as mentioned before is expense of roughly twice that of FLOODED or WET batteries and last only half as long. That makes using them as much as 400% higher cost. Just remember Wet FLA Hybrids can do almost as much as AGM.

    But if you are one of the silly risk takers that insist on a 12 volt battery with a 1000 watt monster Inverter, you need AGM. Just pray you terminated the connections correctly.

    Parallel Battery Arrangements should be avoided to obtain required AH capacity unless necessary. Very rarely is it necessary as battery AH capacity varies from 10 to 4000 AH. Without going into a lot of detail the reason boils down is you will significantly shorten battery cycle life. When you parallel batteries you cannot equalize the the currents. This forces 1 string to do most of the work, leaving the other strings to be under worked. The end result weakens all the batteries and shorten cycle life.
    MSEE, PE

  • #2
    At the request of the originator, this tutorial sticky thread has been restored to its pristine state as it was back in 2013.
    New developments of interest will be added by the originator if he chooses to make edits or can be made the topic of new threads.

    When a thread is made sticky it is often because it is useful to others as it stands, and closing the thread reduces clutter that can take away from its value.

    Last edited by inetdog; 09-12-2015, 03:45 AM.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.