Well, 900 cycles at 80% DOD means that the battery will last 900 cycles if discharged 80% down to 20% remaining capacity. A cycle in this case is a discharge of the battery from 100% down to 20% and then recharged back up to 100%.

If the manufacturer is stating this then they have likely already done the test themselves. If you wanted to perform the test yourself, you could monitor the battery voltage to get an idea of state of charge (as long as you had the battery data sheets to reference it to). You would also need a fairly large forced-air cooled (water loads tend to dissolve at dc) resistive load for the discharge, and a changeover system between the load and a suitable battery charger. Generally this is not the sort of test you need to perform (unless the battery brand and quality is not well known).

What is the application.

Dear Friend

Depth of discharge means the extent to which the battery is discharged. Lets take the case of 80% DOD, this means that 80% of the rated capacity of the battery has been removed, before it is recharged, thus 80 Ah for 100 Ah battery.

VERY important factors to be considered for the no. of discharge cycle is (a) rate of discharge, meaning thereby the current at which the battery is CONSTANTLY discharged to arrive at the capacity. (b) end cell voltage, meaning thereby that the battery voltage at the end of the said discharge e.g. 1.75 V/cell for 2.0 V cell. or 1.85 V/cell.

Generally VRLA battery is rated for 20 hours or 10 hours rate of discharge. Thus 100 Ah capacity at 20 hours rate of discharge means that if the battery is discharged at 100/20= 5 Amps., then battery will provide 100 Ah capacity & go down to 100% DOD. However if discharging current is increased then the battery will last for lesser duration, which is disproportionate i.e. if discharged at 20 Amps. then battery will NOT last for 5 hours, it will be much lesser & manufacturer provides the required factor.

No. of cycle means that the no. of such discharge and re-charge, before the battery life is over. Thus 900 cycle means Battery can be discharged and recharged 900 times PROVIDED (a) the battery is discharged at current rate for which the battery capacity is defined ( 10 hours or 20 hours etc., rate of discharge, any other may also be possible ) For other discharge rates, no. of cycles will vary (b) In each DISCHARGE CYCLE ONLY, sufficient amount of ampere hour capacity is removed from the battery corresponding to the defined DOD & then the battery is COMPLETELY RECHARGED BEFORE NEXT CYCLE IS STARTED & (c) In each discharge cycle, the battery voltage at the end of discharge, does not go down below the specified.

The test to check the no. of cycles which the battery can provide is a TYPE TEST called life cycle test. Most of the reputed manufacturers do conduct such tests on certain ranges of battery. Some have inhouse test equipment, others get it done at an outside lab.

I am not aware of the equipment manufacturer but you can try searching for battery life cycle tester on Google or any other engineering search engine or any engineering website which also has manufacturers data.

Trust this clarifies, Pls. do get back, if you have any more querry, and yes, I am not a battery manufacturer, but do make battery chargers ( company is ISO 9001-2000 certified by TÜV ) for power plants, substations etc. with installations in Vietnam, Myanmmar, Bhutan, Indonesia, Malaysia, Bangla Desh, Tanzania & Nepal apart from all over India.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Dear Ashok Toshniwal:

I read that you manufacture battery chargers. Where would I be able to get more information of your chargers?

Regards,

Maksun

Everything was already said is correct.

I would add only that temperature is also to be considered as a derating factor of a battery capacity. Seek curves at the manufacturer.

As for measurements, I would suggest to build your own system with LabVIEW (www.ni.com/labview) or to use DC voltage&current and temperature dataloggers.

If you need more details, just ask.

Good luck!

A small US company, West Mountain Radio, that makes power products primarily for Amateur Radio and Radio Control vehicle hobbyist makes a very nice product called a Computerized Battery Tester that works with your PC and will collect and graph a constant stream of data while discharging your battery at whatever rate (up to 40 amps) you choose, up to 150 watts. That would only be about 12 amps max for a 12 volt battery, but they do have an optional add-on 500 watt amplifier accessory, which would give you about 40 amps capacity at 12 VDC.

The product has a motor driven fan, but I am not sure if that is to cool the resistor, or is itself the load, although an inductive load would not really be a problem for DC.

Here is the text from their webpage at:

http://www.westmountainradio.com/CBA_ham.htm

FEATURES

• Easy to use and foolproof.
• Perform tests like a pro!
• Analyze exact battery characteristics.
• Match cells or pick the best pack.
• Check for battery aging.
• Cycle and condition batteries.
• Test at up to 150 watts or 40 Amps. Plug and Play high speed USB interface, with easy to use and intuitive Windows software supplied on CD ROM. Scientifically analyzes battery performance with a true constant current battery capacity test that is graphically displayed. Perform tests quickly at real world load conditions, up to 150 watts or 40 amps! High voltage testing at up to 48 volts; the equivalent of 1 to 38 NiCad or NiMh cells. Save, display and print battery test graphs and battery labels. Measures and displays voltage, current, amp-hrs, watts and temperature*. Easy overlay comparisons of multiple graphs may be displayed saved and recalled. Test any type of battery: NiCad, NiMH, Lead Acid, Li Ion, Li Poly, Alkaline, Carbon Zinc, Mercury etc; from coin cell to automotive or larger. Accurate measurement with up to 12 bit resolution. Auto selection of two current and three voltage ranges. Each CBA is individually, digitally calibrated, against NBS traceable instruments. On board C8051 based USB Micro controller. Superior, software and electronically regulated, constant current testing using a solid state FET fan cooled electronic load. Automatic test shut off at a safe pre-determined minimum battery voltage. Default shut off voltage may be user overridden. Automatic test shut off at a for a pre-determined maximum battery temperature. (Requires optional temperature probe) Fail safe: software and/or hardware protection of temperature, current, power and reverse polarity. Supplied with USB cable and high grade 13 gauge flexible Powerpole battery test cable. Optional adapters available for most batteries. Optional external temperature sensor provides measurement of battery temperature for complete testing. Maximum test rate: 150 watts or 40 amps, whichever is higher. Discharge test current user selectable from 0 to 40 Amps. DESCRIPTION The CBA is much more than a simple battery voltage tester or a battery load tester. Unlike a simple load tester the CBA will test virtually any type or size of battery, any chemistry, any number of cells up to 48 volts. For the first time and for a reasonable price, anyone can do scientific tests of their batteries by letting their computer do all the work. The CBA is capable of higher test rates than other testers: up to 40 amps or 150 watts, whichever is higher. It not only tests the total amount of energy stored in a battery (capacity in amp-hrs), but it graphically displays and charts voltage versus amp-hours. Unlike a resistor load it has a constant current load that is controlled both with software and electronically. Graphs may be displayed, saved and printed. Multiple graphs of the same battery, or multiple batteries, may be compared or overlaid, a very useful feature. Battery tests may be printed on a color or black and white printer. You may also print convenient test labels to placed directly on your batteries to remember the last time they were tested and how they performed. A CBA will measure the temperature of a battery under test using the optional external temperature probe. The temperature probe will provide automatic over-temperature shutoff a preset temperature limit. The CBA is ruggedly built and it is supplied with high grade wire with Powerpole battery connectors. Other connectors may be installed our you may use our adaptors or make adaptors to the Powerpoles. A CBA is compact and has a high performance cooling system with a quiet fan. LED indicators show test status from across a room. The CBA uses an 8051 based micro controller. Each CBA is individually calibrated to high accuracy. The electronic load uses a pulse width modulation system to control a power MOS FET with electronic and software current regulation. The on-board micro controller provides the plug-and-play USB interface to the computer. The software supplied with the CBA is easy and intuitive to use. It provides automatic sensing of the battery cell count and recommends a safe maximum discharge current and minimum safe cutoff voltage for your batteries. The system of software and hardware is designed to protect both the CBA and the batteries that are tested. We think that you will find the CBA a useful and essential tool for anyone that depends on batteries. You will find that you learn new, valuable, information about your batteries that cannot be determined any other way. Using batteries without a CBA is like driving a car without a gas gauge.

  SPECIFICATIONS

  Maximum continuous discharge rate: 100 watts Maximum limited term discharge rate with < 3500 ma-hour battery: 125 watts Maximum limited term discharge rate with < 1000 ma-hour battery: 150 watts 0-3 amp accuracy: typically better than + - 10 ma (12 bit, NEW! CBA II) 3-40 amp accuracy: typically better than + - 45 ma (10 bit resolution) 0-5 volt accuracy: typically better than + - .005 volts (10 bit resolution) 5-10 volt accuracy: typically better than + - .01 volts (10 bit resolution) 10-50 volt accuracy: typically better than + - .05 volts (10 bit resolution) Absolute maximum operating voltage: 48 Volts Maximum discharge rate: 40 amps (3.75 Volts at test start)(Battery dependant) Minimum Voltage for a 40 amp discharge: 2 volts at completion of test (Battery dependant) Minimum discharge rate: Zero! May be used for charge cycle monitoring. (NEW! CBA II) Residual current drain, battery connected while not in use: < .003 amps @ 12 volts User selected battery cell chemistry, number of cells and test current, with automatic graph setup and scaling. High performance C8051 based micro controller with built in USB interface and 10 bit A/D conversion. USB powered; the CBA does not use the battery being tested to run the CBA or the fan. Software calculates and recommends safe tests based on the user supplied battery information. Supplied with USB cable, Powerpole battery connectors and Windows compatible software CD with full documentation. System ready and Test in progress LED indicators, viewable from across a room. Automatic voltage shut off at end of test using a software recommended or user selected safe discharge voltage. Automatic temperature shut off at end of test at using a software recommended or user selected maximum temperature. Optional external magnetic temperature sensor required for temperature measurement and/or battery auto over-temp shutoff. Internal automatic over temperature shutoff. Graph printing on any standard color or B&W printer. Battery test label printing on standard 05160 stick-on labels. Dimensions: 3.5" H x 2.8" W x 3.6" D. Weight: 16 oz.

  Computer System Requirements

  Minimum Requirements: A PC 233 MHz or better
  At least a 800 X 600 graphics card and display monitor
  Windows 98SE, ME, NT, 2000, XP with necessary RAM
  An available USB 2.0 or USB 1.1 port. Recommended: A PC 1 33 MHz or better.
  Better than 800 X 600 graphics card and display monitor.
  Windows W2000, XP with 128 MB RAM or better
  An available USB 2.0 or USB 1.1 port. For graph and label printing: Any Windows compatible, laser or ink jet, color or black and white, printer.
  Avery 05160 labels are required for label printing.

Hello, I wish to add two comments to what been already said:

First of all, avoid discharging your battery under the 80% DOD. Over that discharge rate the temperature of the battery increases and damages your plates, which will shorten the life of your battery (less cycles). This may be controlled by the use of a BDI (Battery Discharge Indicator).

As to measuring the cycles, there is a manufacturer of an instrument capable of telling you the % of life left in your battery, but not the number of cycles, as this will depend on the use that you give it. I will recommend that you ask the battery manufacturer for the chart that would give you estimated life cycles at different outputs. I will see if I can remmenber were I saw the information of the instrument capable of measuring you battery.

Good Luck

Maksun