Equus 3721 Battery and Charging System Monitor

• Displays the condition of the battery and charging system
• Designed for 12-volt negative ground systems
• Protects the engine computer and 12-volt accessories from surges
• Easily plugs into a cigarette lighter or power receptacle
• Head pivots for easy viewing and angle adjustment

The picture on Amazon site is not correct. This battery monitor shows the voltage value with .01 precision (or two digits after decimal point). That is far more then enought to tell the battery status. I put it in the car, it automatically switches between "battery status monitoring" and "charging status monitoring". When the engine is stopped, it is in "battery status monitoring mode", when engine is running, it will be in "charging status monitoring" mode. Amazon's price is even bettern then Walmart. Definitely a great value buy. Will recommend this item to my friends.

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Seemingly just another auto gadget fortunately the Equus 3721 is more sophisticated than its ponderous description. A breeze to connect to any car's 12 Volt electrical system. Simply push into the lighter socket or an auxiliary power outlet now found in many newer vehicles.

With the engine running the instrument constantly displays battery condition with an LED light; amber when marginal, red if the battery is discharging. A green light indicates a correctly functioning electrical system. All is well with both battery and, most importantly, the alternator.

The Equus is also an accurate voltmeter. Digital read-outs give exact voltage in the electrical system. Potential alternator problems or a failing battery will be indicated by below normal voltages, plus an amber or red light. Extra information is a battery icon graphically showing total battery charge. Tending towards erratic read-outs, and therefore unreliability, it is not the unit's best feature.

Equus's instruction card is easy to understand. The unit is well made, sturdy, easy to connect and to transfer to any 12 volt system not having its own voltmeter. Also, as a supplemental monitor in an RV, or a bigger boat with a remote 12 Volt outlet in a sleeping area far from the main instrument panel, overall battery condition condition can be monitored while camping or at anchor.

Good value for money; very useful. From personal use, recommended.

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The Honda 2005 civic has a marginal charging system. This meter is ideal for determining when it is time to turn off the radio to reduce load on the alternator. Voltage reading is very accurate, much better than 1% as measured against a small Beckman pocket meter, which in turn has been checked against a Powerex Wizard aa cell charger. Warning lights function well.

Some things to note when using this tester: Standard voltage of a 12 volt battery is 12.6 volts. Some deep cycle absorbed glass mat batteries will read 12.8. This is after loading the battery by turning on the headlights for 10 seconds, to remove surface charge. Note that while the lights are on, the voltage drops quickly at first, then the voltage stabilizes. Turning off the lights causes the voltage to rise again gradually. After a few minutes the voltage will stop rising. If the voltage settles at 12.6 (or 12.8 for AGM battery) battery is charged, assuming that the battery is near 68 degrees F. Lower temps raise the voltage, higher temps lower the voltage. For a standard battery figure about 12.66 volts at 32 F and 12.54 volts at 104 F battery temperature, not air temperature.

After a car has been running for awhile with no lights, radio, wipers, AC, heat or window defroster, the alternator may cycle letting the battery voltage drop for a while before kicking in. This is OK provided the charging is steady shortly after turning on the lights. An intermittant alternator will cause the red light to turn on and off when headlights are on.

The bar graph for battery condition is not very useful as the meter has only voltage information.

The instructions do not state that this tester is for negative ground cars only, a small quibble as positive ground is not common.

Had I bought this device six months ago I could have avoided killing a brand new battery in six months.

UPDATE: Still working fine as of Aug 2, 2012

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I purchasted this unit to use in a small aircraft that has no built in battery monitor.

The unit failed within one hour of use.

It was too cheap to bother to send back so I took it apart.

I found two loose screws holding the circuit board and display in place and a bad solder joint.

I repaired the solder joint and tightened the screws and the unit has been working fine ever since.

Unless you are an Electronic Engineer like me I would not recomend this unit.

Strangely enough, the internal components appeared to be high guality.

It was not assembled correctly.

It's OK if it works.

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just got the monitor from amazon based on the reviews here. the actual device is slightly different from it looks in the picture, with rounder edges. i guess the new product has been revised. also the protective plastic film is extremeply easy to peel off, a bit too easy i would say. or it might have something to do with the weather. here in singapore it's 30C all the time. the device has good build quality. the monitor can show two different tiny icons above voltage reading, under the battery and charging modes. the LCD is clear with bright blue backlight. basically it doesnt cost arm or leg but does all i expected. i will leave it plug in all the time in my car. i am sure i will be alerted by the unusual low voltage one day to realise the time to replace my battery. that will be the time i can recover the cost of this product by saving the expensive recovery service.