How to Check a Car Battery

Check a Car Battery

Here you can get How to Check a Car Battery and checking methods for Car Batteries.

Most car batteries are sealed for life – apart from a small vent hole which allows gas to flee. They never need topping up. The fluid level in other batteries should be checked a minimum of once a month and topped up if it drops below the right level – just above the tops of the battery plates. Never top up with water, which contains minerals which can damage the battery. Use distilled or otherwise purified water, or a proprietary topping-up fluid.

Avoid over-filling, which causes the electrolyte to leak through the cell-cap vents because the battery is charged. Do not use a unadorned flame when checking the battery. The fluid inside – called the electrolyte – can give off explosive gas, especially soon after the battery has been charged. The electrolyte may be a mixture of vitriol and purified water, and is corrosive and dangerous. don’t allow any to splash on to your skin or your clothing. If you’re splashed, wash the affected skin area immediately. If it goes in your eye, wash thoroughly in running water and call a doctor.

If electrolyte splashes on to your car, hose it off immediately. A drop by the battery fluid level is caused – as long as there are not any leaks – by evaporation of the water within the electrolyte mixture. Once the extent falls below the tops of the battery plates , the cell concerned starts to lose efficiency. If the cell is left for a few time with the plates exposed, it are often damaged. That successively will ruin the battery, which needs all its cells functioning to retain its full electrical charge and deliver power. The battery must get replaced.

How quickly the electrolyte evaporates depends an excellent deal on two factors: the under-bonnet temperature (if the battery is found there); and whether the generator is overcharging the battery. Generally, the upper the temperature the more frequently A battery may have topping up. In most cases, the monthly check is enough – but check more often in weather, or if the extent is well down at the monthly check. Battery cases rarely leak. If more than the usual amount of topping up suddenly becomes necessary, search for the cause. If a charging-system fault is overcharging the battery, you’ll find damp patches round the cell caps and even droplets of electrolyte on the battery top (See the way to test a automobile battery ).

How to top up a battery

Remove the cell caps or trough cover and fill each cell to the level marked on the battery case. If there’s no mark, fill until the electrolyte just covers the battery plates, which you’ll see through the filler holes. Apart from distilled or otherwise purified water, proprietary topping-up fluids are available from garages, accessory shops and sometimes chemists. Buy them only in sealed containers, to make certain that they’re not contaminated.

As an alternative, water from a de-frosted refrigerator are often used, but it must be kept in a clean glass jar or bottle. Always keep the battery top clean – wipe it before removing the cell caps or trough cover, when dirt is liable to fall under the cells. The cell caps or cover have ventilating holes to permit the escape of gases when the battery is being charged. make sure these holes are clear. After topping up, wipe away any water spilled on the top of the battery.

Using a hydrometer

You can find out how well A battery is charged by measuring the specific gravity – or density of the electrolyte, which varies according to the state of charge. The specific gravity is that the weight of a specific volume of liquid compared with that of an equivalent volume of water. The figure for electrolyte during a fully charged battery is between 1.270 and 1.290 – meaning that it’s 1.270 times heavier than water. However, because the battery loses charge, the precise gravity drops to 1.130 or lower.

The instrument for measuring relative density may be a hydrometer , which contains a weighted float . The float is marked with a graduated scale , usually reading from 1.10 to 1.30. Insert the syringe into a cell, then squeeze and release the bulb to draw up a sample of electrolyte – enough to raise the float but not enough to form it touch the bulb. Read off the graduation mark which is level with the surface of the electrolyte.

The state of charge are often gauged from what proportion the figure is below 1.290. A reading of, say, 1.200 would show the battery to be about half charged. The float could also be graded red, yellow and green to point out low, half or full charge. Some hydrometers have three small balls of various weights rather than a float. the amount of balls that float to the highest of the sample indicate the state of charge. After taking the reading, squeeze the bulb to return the electrolyte to its cell, and test the opposite cells successively . All should give similar readings within about 0.04 of every other – any greater variation indicates a defective cell, and therefore the battery must be replaced. The best time for testing is after the battery has been charged or the car run about half-hour . cut the engine and lights.

Check Your Battery with a Voltmeter

  • Turn your ignition off.
  • Remove the battery’s positive terminal cover. Check and clean the battery terminals.
  • Connect your voltmeter’s positive lead to the positive terminal on your battery. The positive lead on a voltmeter is usually red.
  • Attach the negative voltmeter lead to the negative battery terminal.
  • Check the voltmeter. If your battery is in good condition, the voltage should be between 12.4 and 12.7 volts. A reading lower than 12.4 volts means that your battery needs to be charged.
    • If the reading is lower than 12.2 volts, “trickle charge” the battery, which is a slow charge. And then re-check.
    • If the reading is over 12.9 volts, you have excessive voltage. Turn on the high beams to remove excessive voltage surface charge. Over voltage may be an indication the alternator is over charging the battery.
    • While you have the voltmeter handy, you may also want to do load testing.

Check Your Battery with a Power Probe

  • Remove the battery’s positive terminal cover.
  • Connect your Power Probe’s positive lead to the positive terminal on your battery. The positive lead on a voltmeter is usually red.
  • Attach the Power Probe’s negative lead to the negative battery terminal.
  • Connect the tip of the probe to the positive battery terminal. Check the probe for voltage reading.
  • Check the Power Probe reading. If your battery is in good condition, the voltage should be between 12.4 and 12.7 volts.

Check Your Battery by Cranking the Engine

  • “Crank” the engine by turning the ignition until the starter engages and hold for 2 seconds Have an assistant crank the engine while you check battery voltage drop.
  • At the time of the crank, check the reading of the Power Probe. It should not go below 9.6 volts.
    • A battery with a volt reading less than 9.6 volts means the battery is sulfated and not holding/accepting the charge.


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