Tech Tips

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Electrical System

BATTERY TESTING & CHARGING

(1) CHARGE!!
Whenever a vehicle exhibits symptoms of a charging or starting system failure, the most basic test which should be performed first is a visual and voltage test of the battery. Knowing the exact condition of the battery is the best way to know whether or not to suspect other system components and can prevent the unnecessary installation of a Starter or Alternator. Even a Bosch Premium Quality Remanufactured Starter or Alternator cannot repair a faulty shorted battery!

(2) WHERE DO WE START?
To analyze the condition of a battery very little "High Tech" equipment is really needed. while there is excellent equipment available for big "$$$$", all that is really needed is a good DVOM (Digital Volt Ohm Meter), a battery charger, some patience and a little common sense.

(3) HOW MUCH CHARGE IS ENOUGH?
If the battery you are working on does not have one of the "EYES", you can determine the current charge by placing the leads of a DVOM across the two battery terminals, after turning off all accessories. This reading is the STATIC VOLTAGE of the battery. If the STATIC VOLTAGE is less than 12.5 volts the battery must be recharged.

(4) HOW LONG WILL IT TAKE?
If you have one of the more expensive electronically controlled battery chargers the proper length of time and charging rate will be taken care of for you. If not, it is important that you determine the STATIC VOLTAGE of the battery and determine how long to charge the battery. (see #3 above) Do not charge a battery more than 10% of its AMP hour rating as this "fast charging" can be harmful to the longevity and proper operation of the battery!

(5) CHARGE TIME
By checking the STATIC VOLTAGE with the figures in the following chart you can determine the discharge percentage of the battery.

Now that you know the STATIC VOLTAGE and the percent of discharge, the following formula can be used to determine how long to charge the battery:

Battery Size* x % discharged
10% of Battery Size

*Amp hour rating of battery. Usually the battery size is printed on the battery and is given in an A/H (amp/hour) rating such as 60AH

For example, a 60 A/H battery which as a STATIC VOLTAGE of 12.5V is 25% discharged according to the chart. So:

60 A/H x .25 = 15 = a charge time of 2.5 hours
         6                  6

(6) NOW THAT IT'S CHARGED, IS IT STILL GOOD?
Just because you have recharged the battery, that is no guarantee that the battery is still good, and has more than just a few starts left in it. You might get it out of the shop only to have it die on the road! After recharging, the battery must be LOAD TESTED to ensure that it has the ability to maintain enough cranking capacity under load.

(7) HOW DO YOU LOAD A BATTERY?
If you already own a battery load tester follow the manufacturer's instructions and determine if the battery is still good. If this equipment is not available, an accurate and reliable battery load test may be performed by following these steps.

1. Disconnect ignition coil wire.
2. Jumper ignition coil wire to ground.
3. Connect volt meter across battery.
4. Observe battery voltage on volt meter while cranking battery for 15 seconds.
5. Depending upon ambient temperature* of battery, if battery voltage falls below 9.6 volts, battery should be discarded and replaced.

*Temperature has a definite effect upon a battery's condition; refer to the following Temperature/Voltage chart when load testing a battery. Colder temperatures will decrease the reading you get when load testing a battery

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