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Frequently Asked Questions about Batteries

Frequently Asked Questions (FAQ) About Batteries

 

 

 

 

1) BATTERY RATINGS

How are batteries rated and what do the ratings mean in battery selection?

ANSWER:
The most common battery rating is the AMP-HOUR RATING. This is a unit of measurement for battery capacity, obtained by multiplying a current flow in amperes by the time in hours of discharge. (Example: A battery which delivers 5 amperes for 20 hours delivers 5 amperes times 20 hours, or 100 ampere-hours.)

Manufacturers use different discharge periods to yield an different Amp-Hr. Rating for the same capacity batteries, therefore, the Amp-Hr. Rating has little significance unless qualified by the number of hours the battery is discharged. For this reason Amp-Hour Ratings are only a general method of evaluating a battery's capacity for selection purposes. The quality of internal components and technical construction within the battery will generate different desired characteristics without effecting its Amp-Hour Rating. For instance, there are 150 Amp-Hour batteries that will not support an electrical load overnight and if called upon to do so repetitively, will fail early in their life. Conversely, there are 150 Amp-Hour batteries that will operate an electrical load for several days before needing recharging and will do so for years. The following ratings must be examined in order to evaluate and select the proper battery for a specific application: COLD CRANKING AMPERAGE and RESERVE CAPACITY are ratings used by the industry to simplify battery selection.

 

2) COLD CRANKING AMPERAGE:

How does the Cold Cranking Amperage rating help me select a battery?

 ANSWER: 

(CCA) is the maximum amperes that can be continuously removed from a battery for 30 seconds at 0°F before its voltage drops to unusable levels. A 550 CCA battery can supply 550 amperes for 30 seconds at 0°F. This rating is only useful in the selection of engine starting batteries.

NOTE: Do not confuse Cold Cranking Amperage (CCA) with Marine Cranking Amperage (MCA) or Cranking Amperage (CA). MCA and CA is a higher battery rating measured at warmer temperatures.

 

3) RESERVE CAPACITY

What does the Reserve Capacity rating mean and how does it apply to deep cycle batteries?

ANSWER:
Reserve capacity is the number of minutes a battery can maintain a useful voltage under a 25 ampere discharge. The higher the minute rating, the greater the battery's ability to run lights, pumps, inverters, and electronics for a longer period before recharging is necessary. The 25 Amp. Reserve Capacity Rating is more realistic than Amp-Hour or CCA as a measurement of capacity for deep cycle service. Batteries promoted on their high Cold Cranking Ratings are easy and inexpensive to build. The market is flooded with them, however their Reserve Capacity, Cycle Life (the number of discharges and charges the battery can deliver) and Service life are poor. Reserve Capacity is difficult and costly to engineer into a battery and requires higher quality cell materials.

For instance, Rolls, Surrette and Lifeline use thicker lead grids (the plate's skeletal structure) to support additional positive plate oxides which are compressed into a denser form in order to add battery reactive material for greater Reserve Capacity and Cycling Performance. In addition, these plates are separated by indestructible separators. These mats hold the active oxides tightly in place during the cubical plate expansion which occurs during deep discharging, instead of allowing the oxides to shed off and precipitate to the bottom of the battery. Construction materials such as those raise the Reserve Capacity of a battery and increase the battery's Cycle Life.

 

4) CYCLE LIFE

What is battery cycle life?

ANSWER: 
One cycle of a battery is a discharge from full charge to full discharge and a return to full charge again. The total number of cycles a battery can perform before failure is called its Cycle Life. Most battery manufacturers will not discus the Cycle Life of their product. Many advertised Deep Cycle batteries have not been tested, or, which is the case with cranking batteries, were never designed for long Cycle Life .

 

5) DEEP CYCLE BATTERIES

What is the difference between deep cycle batteries and starting batteries?

ANSWER:
Unfortunately, the term Deep Cycle has been overused by the battery industry as a sales tool to imply a heavy duty product. This has led to confusion and difficulty in battery selection. One must understand that any battery may be termed deep cycle as all batteries may be fully discharged and charged. However, a true deep cycle battery, such as Rolls or Lifeline, is capable of thousands of these hard cycles during its life without losing its capacity. Comparatively, many advertised deep cycle batteries composed of thin plates, excessively porous separators, and low density plate oxides will suffer permanent capacity loss after a few dozen cycles and will shortly sulfate or shed plate material and fail. Batteries without substantial materials designed for true deep-cycling will lose more than half of their capacity after only a few cycles. A 200 Amp-hour battery will shortly become a 100 Amp-hour battery for the remainder of its shortened service life. What initially may seem to be an inexpensive battery to purchase, now costs twice as much per Amp-hour. True Deep cycle batteries will perform well as cranking batteries, however, cranking batteries will not survive deep cycle use.

Deep cycle batteries can be used in any application and exhibit a long service life, while cranking batteries are limited to starting applications only. Cranking batteries exhibit poor service life in cycling applications.

 

6) INCREASING CAPACITY THROUGH SERIES AND PARALLEL CONNECTIONS

What is the difference between series battery connections and parallel battery connections and how do they increase battery capacity and voltage?

ANSWER: 
In the SERIES CONNECTION, batteries of like voltage and Amp-Hour capacity are connected to increase the Voltage of the bank. The positive terminal of the first battery is connected to the negative terminal of the second battery and so on, until the desired voltage is reached. The final Voltage is the sum of all battery voltages added together while the final Amp-Hours remains unchanged. The bank's Voltage increases while its Amp-Hours, Cranking Performance and Reserve Capacity remain unchanged.

In the PARALLEL CONNECTION, batteries of like voltages and capacities are connected to increase the capacity of the bank. The positive terminals of all batteries are connected together, or to a common conductor, and all negative terminals are connected in the same manner. The final voltage remains unchanged while the capacity of the bank is the sum of the capacities of the individual batteries of this connection. Amp-Hours Cranking Performance and Reserve Capacity increases while Voltage does not.

 

Picture: Series and parallel battery connections.
7) BATTERY MAINTENANCE

Does overcharging damage batteries?

ANSWER: 
OVERCHARGING is the most destructive element in battery service. Usually the boater is not aware that this is occurring as he believes his alternator or battery charger is "automatic." Unfortunately, these automatic circuits are sensitive to voltage surges, heat, direct lightening strikes and indirect lightening electromagnetic influences and could fail or shift their calibration. When they fail, overcharging begins to effect the batteries. During overcharging, excessive current causes the oxides on the plates of the battery to "shed" and precipitate to the bottom of the cell and also heat the battery, thus removing water from the electrolyte. Once removed, this material (which represents capacity) is no longer active in the battery. In addition, the loss of water from the electrolyte may expose portions of the plates and cause the exposed areas to oxidize and become inactive, thus reducing additional capacity. Sealed batteries are not immune from the same internal results when overcharged. In fact, sealed recombination absorption and gel batteries are particularly sensitive to overcharging. Once moisture is removed from the battery, it cannot be replaced. Portions of the battery damaged due to overcharging are irretrievable. However, if detected early, corrective adjustments to the charging device will save the undamaged portion of the battery. Initial signs of overcharging are excessive usage of water in the battery, continuously warm batteries, or higher than normal battery voltages while under the influence of the charger. If overcharging is suspected, correct immediately.

 

8) OVER-DISCHARGING

Does over-discharging damage batteries?

ANSWER:
OVER-DISCHARGING is a problem which originates from insufficient battery capacity causing the batteries to be overworked. Discharges deeper than 50% (in reality well below 12.0 Volts or 1.200 Specific Gravity) significantly shorten the Cycle Life of a battery without increasing the usable depth of cycle. Infrequent or inadequate complete recharging can also cause over-discharging symptoms called SULFATION. Despite that charging equipment is regulating back properly, over-discharging symptoms are displayed as loss of battery capacity and lower than normal specific gravity. Sulfation occurs when sulfur from the electrolyte combines with the lead on the plates and forms lead-sulfate. Once this condition becomes chronic, marine battery chargers will not remove the hardened sulfate. Sulfation can usually be removed by a proper desulfation or equalization charge with external manual battery chargers. To accomplish this task, the flooded plate batteries must be charged at 6 to 10 amps. at 2.4 to 2.5 volts per cell until all cells are gassing freely and their specific gravity returns to their full charge concentration. Sealed AGM batteries should be brought to 2.35 volts per cell and then discharged to 1.75 volts per cell and their this process must be repeated until the capacity returns to the battery. Gel batteries may not recover. In most cases, the battery may be returned to complete its service life.

CHARGING Alternators and float battery chargers including regulated photo voltaic chargers have automatic controls which taper the charge rate as the batteries come up in charge. It should be noted that a decrease to a few amperes while charging does not mean that the batteries have been fully charged. Battery chargers are of three types. There is the manual type, the trickle type, and the automatic switcher type.

 

9) BATTERY ELECTROCHEMISTRY EVALUATION

How can I evaluate the health and charge state of a battery?

ANSWER:
Routine battery examinations divulge irregularities in the charging system as well as in the batteries. The principle method is to examine the electrochemistry of the battery through hydrometric electrolyte inspection. As previously discussed, this important examination cannot be accomplished with sealed absorption or gel batteries. Voltage readings alone require experience to interpret. Hydrometric readings will uncover early warnings of overcharging or over-discharging before batteries are damaged. The state-of-charge and reliability of a lead acid battery can best be determined by the specific gravity of the electrolyte measured directly with a common bulb-type hydrometer with a glass float. We do not recommend the ball float type hydrometer. Specific gravity is a unit of measurement for determining the sulfuric acid content of the electrolyte. The recommended fully charged specific gravity of marine batteries is 1.255 to 1.265 taken at 80°F. More than .025 spread in readings between fully charged cells indicates that the battery may need an equalization charge. If this condition persists, the cell is failing and the battery should be replaced. Since water has a value of 1.000, electrolyte with a specific gravity of 1.260 means it is 1.260 times heavier than pure water while pure concentrated sulfuric acid has a specific gravity of 1.835.

The following table illustrates typical specific gravity values for a cell in various stages of charge:

 

100% Charged.......1.255 - 1.260 Sp. Gr.

 75% Charged.......1.220 - 1.225 Sp. Gr.

 50% Charged.......1.185 - 1.190 Sp. Gr.

 25% Charged.......1.150 - 1.155 Sp. Gr.

  0% Charged.......1.115 - 1.120 Sp. Gr.

Temperature compensation of hydrometric readings is usually unnecessary unless the battery is extremely hot or cold, however, after hard charging or discharging, you may want to add or subtract points of Specific Gravity based on the table.

 

Do not apply hydrometer color coding to readings taken from deep cycle batteries. These red-white-green markings are for "hot" automotive battery types. Also, hydrometer readings taken immediately after water is added to a cell is inaccurate. The water must be thoroughly mixed with the underlying electrolyte by charging, before hydrometer readings are reliable. In addition, do not assume a deep cycle battery will not take a charge because you have been charging it for a while and the float will not rise. If the battery has been fully discharged or partially sulfated it will require considerable charging or equalization before recovering. As electrolyte levels are reduced in the battery, it is important to add water to each cell. Note that only the water portion of the electrolyte evaporates, therefore, it is not necessary to add acid to a battery during maintenance. In fact, the addition of acid to an active battery will reduce its capacity and shorten its remaining life. Water should be added to cells after charging the battery. This will eliminate spillage due to expansion of electrolyte upon charging. Generally speaking, any water that is safe to drink is safe to use in a battery. Do not use water of a known high mineral content or stored in metallic containers. It is the metal impurities in the water that lower the performance of the battery. Distilled water guarantees purity.