How to test and charge your battery.
Without the right testing equipment it can be very difficult to test a battery. The easiest method is to measure the specific gravity by using a hydrometer and to measure the voltage using a digital multimeter, if you test a lot of batteries you may need to buy a good load tester.
First you must charge the battery (see below). Check the battery voltage after removing any surface charge, it should read above 12.65 volts for a fully charged battery, if your battery is measuring 10.5 volts after charging it typically indicates a shorted or faulty cell. If you can check every cell in the battery with a hydrometer, the cell readings should all be the same, a fully charged cel reads 1.265 - 1.280, if there is more than 0.05 points different it indicates a faulty battery. Readings below 1.225 indicate the battery needs to be charged before load testing.
If the battery is sealed it should have a built in hydrometer telling the charge of one cell, you may get a good reading in that cell but the problem may be in one of the other cells.
Once the battery is charged you need to use a load tester. A good load tester is very expensive so it may be better to get a professional to test it.
Vehicle alternators are a very basic battery charger, they can recharge you vehicle battery if it is not deeply discharged. If your battery is deely discharged it is highly recommended to recharge on an automatic or "smart" charger. These chargers have multiple stages of charging and some offer different modes depending on the type of battery you are charging. Wet, Calcium, AGM and Gel batteries all like different voltages check with the battery supplier for more info on suggested charge voltages.
Before charging check the electolyte levels and top up with distilled water if necessary. Connect the charger leads to the battery terminals red positive lead to the positive terminal and the black negative lead to the negative terminal, make sure they are on the correct terminals as it is possible for the charger to reverse the polarity in the battery if hooked up incorrectly. Only turn on the charger once it is connected to the battery. Never touch the charger leads when the charger is on and turn the charger OFF before disconnecting the leads.
Batteries should be monitored whilst on charge, if the battery is faulty there is a good chance the charger will not switch off and the battery will overheat and be overcharged. If the battery has a faulty cell the charger will continue to charge the battery until a predetermined voltage in the charger is reached. If the battery has a faulty cell the charger cannot reach this voltage and will contiune to charge until it is manually switched off. You must be very cafeful when handing the battery in this state as a large amount of hydrogen gas would be around the battery and any spark can set off an explosion.
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