Interesting Info about batteries
Cycle Life
How many cycles should a marine/RV-deep cycle battery produce in its life?
Battery cycle life is difficult to calculate and is dependent on many variables. Some of the variables include battery maintenance, recharging battery depth of discharge, battery temperature, cycling use, vibration and overall care and consideration.
One of the most important factors is the amount (in percent) of battery Depth Of Discharge (DOD) level per cycle. As the amount of DOD is increased per cycle, there is a resulting decrease in the amount of total cycle life and available performance retention. If, for example, a battery is discharged consistently to 100% DOD (considering all other variables are consistent), the battery's total cycle life could be much less than one half of a battery discharged to only 50%. Therefore, to optimize performance of a marine/RV-deep cycle battery, it is recommended that the consistent discharge level not fall below 50%. Remember, many other factors effect battery cycle life. If the battery is operating in a high heat environment, (consistently above 90°F) the typical number of cycles could be drastically reduced.
Typical Life Cycle Performance
(Deep Cycle) |
% DEPTH OF CHARGE |
CYCLES TO 50% CAPACITY |
25 |
2200 |
50 |
1000 |
75 |
550 |
100 |
325 |
Determining Battery Depth of Discharge
State of Charge
Battery DOD (in percent) is the opposite of battery state of charge. For example, if the battery is 70% state of charge, the depth of discharge is 30% since the total must be 100%. The most efficient means of determining the battery's state of charge/depth of discharge on removable filler cap batteries is by using a hydrometer, or an accurate digital voltmeter can be used.
Surface Charge: Surface Charge, in general terms, refers to an inflated charge level immediately after the battery has been charged. Surface charge affects a voltmeter test of the battery's state of charge level more than a hydrometer test. As an example, testing the battery voltage-even hours after a charge-and reading 12.66 volts, may not be a true indicator that the battery is fully charged. To remove battery surface charge, it is recommended to apply a load to the battery for a period of time. For example, 10-15 amps for two to three minutes, then allow the battery to sit for one minute before retesting, or you can allow the battery to sit for eight hours with no load or charger connected, then check the voltage.
Ratings and Specifications
Marine/RV-deep cycle batteries have rating specifications which include cold cranking amps (CCA), marine cranking amps (MCA), reserve capacity (RC) and ampere hours (Ah). RC and approximate Ah ratings may not be listed on the battery decal. However, they are available through your local battery distributor. Unless specified, the Ah ratings are based on a 20-hour discharge.
Cold cranking amps (CCA) The amount of current (amps)a battery at 0°F (-17.8°C) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12-volt battery).
Marine cranking amps (MCA) The amount of discharge current a battery tested at 32°F (0°C) can deliver for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts on a 12-volt battery).
Reserve capacity (RC) The amount of time a battery can deliver 25 amps at 80°F (26.7°C) without falling below 1.75 volts per cell (10.5 volts on a 12-volt battery).
Amp Hour (Ah) The Amp Hour rating tells you how much amperage is available when discharged evenly over a 20 hour period. The amp hour rating is cumulative, so in order to know how many constant amps the battery will output for 20 hours, you have to divide the amp hour rating by 20. Example: If a battery has an amp hour rating of 75, dividing by 20 = 3.75. Such a battery can carry a 3.75 amp load for 20 hours before dropping to 10.5 volts. (10.5 volts is the fully discharged level, at which point the battery needs to be recharged.) A battery with an amp hour rating of 55 will carry a 2.75 amp load for 20 hours before dropping to 10.5 volts.
|
percentage of charge remaining |
12 volt battery voltage |
|
100 |
12.70 |
|
95 |
12.64 |
|
90 |
12.58 |
|
85 |
12.52 |
|
80 |
12.46 |
|
75 |
12.40 |
|
70 |
12.36 |
|
65 |
12.32 |
|
60 |
12.28 |
|
55 |
12.24 |
|
50 |
12.20 |
|
40 |
12.12 |
|
30 |
12.04 |
|
20 |
11.98 |
|
10 |
11.94 |
You should recharge a deep cycle battery as soon as possible after each use. It is very hard on a deep cycle battery to sit for extended periods in a partially charged state. To charge the battery, you can use a wide variety of methods. Most RVs provide some sort of converter/charger to "charge" the batteries when you're plugged into an A/C source. Most rigs also have some sort of provision to charge the house batteries from the motorhome or tow vehicle engine. 1. Shallow discharges will result in a longer battery life.
2. 50% (or less) discharges are recommended.
3. 80% discharge is the maximum safe discharge.
4. Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.
5. Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice.
6. Do not leave batteries deeply discharged for any length of time.
7. lead acid batteries do not develop a memory and need not be fully discharged before recharging.
8. Batteries should be charged after each period of use.
9. Batteries that charge up but cannot support a load are most likely bad and should be tested.
If any specific gravity reading still registers lower than the factory specification of 1.277 ± .007 then one or more of the following conditions may exist:
1. The battery is old and approaching the end of its life.
2. The battery was left in a state of discharge too long.
3. Electrolyte was lost due to spillage or overflow.
4. A weak or bad cell is developing.
5. Battery was watered excessively previous to testing
Batteries in conditions 1 - 4 should be taken to a specialist for further evaluation or retired from service.
|
percentage of charge remaining |
12 volt battery voltage |
|
100 |
12.70 |
|
95 |
12.64 |
|
90 |
12.58 |
|
85 |
12.52 |
|
80 |
12.46 |
|
75 |
12.40 |
|
70 |
12.36 |
|
65 |
12.32 |
|
60 |
12.28 |
|
55 |
12.24 |
|
50 |
12.20 |
|
40 |
12.12 |
|
30 |
12.04 |
|
20 |
11.98 |
Small Chart for use in Camper:
|
10 |
11.94 |
|
|
|
Battery Depth of Discharge versus battery lifetime 
Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film. The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.
(From Concorde Battery website)
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