Headlights dim excessively when A/C or other elecrical loads are turned on
Engine turns over slowly (especially in cold weather)
Instrument panel warning light stays on or show intermittent flashing
You have to get jump started without a good reason (like you left your lights on)
You have alternator or belt problems
The battery posts or connecting cables are corroded
Battery life is affected by how and where you drive:
Short trips that don't give the charging system time to recharge your battery fully
A lot of travel on rough roads. The vibration can cause excessive plate corrosion inside the battery
Driving in hot climates (southern Florida or desert climates would be worst) causes accelerated corrosion of the battery plates making batteries last longest in the north and shorter as you head south. A typical battery will last 55 months in the north, but only 38 months in the south.
Batteries contain sulfuric acid, which can burn skin and cause blindness if you get it in your eyes. When charging, batteries can give off hydrogen gas which can ignite if there is a spark.
Always wear goggles or a face shield.
Never lean over a battery when charging, testing, or jump-starting an engine.
Always disconnect the negative cable first and reconnect it last.
Charge batteries only in well-ventilated areas.
Never charge or jump-start a frozen battery; let it warm to at least 40 degrees Fahrenheit.
Keep your battery posts clean of corrosion. Clean them with a wire brush and then coat them with a light coating of high temperature grease.
Keep the connections on tight, Inadequate metal contact causes corrosion on the terminals: When current passes through poor or loose electrical connections, a form of corrosion may form.
Keep the top of the battery clean of heavy dirt and oil with a cloth dampened by a 50/50 solution of baking soda and water. Then rinse with clear water and allow to thoroughly dry.
Maintenance Free batteries don't need water, but if you have a standard battery, then you will need to check and add water periodically.
Check the water level every couple of months. It should be just touching the bottom of the refill hole.
Refill the battery, when needed, with distilled water. Don't use tap water, which produces corrosion on the terminals.
Don't overfill the cells. Just to the bottom of the refill hole is perfect.
Overfilling a standard maintenance battery with water, or over charging a battery can cause excessive corrosion.
Standard batteries are recommended in the south so that the water level can be checked and refilled periodically. A low-maintenance battery with removable vent caps has advantages over a sealed no-maintenance battery because access to the cells allows you or your mechanic to:
Extend the life of your battery when water evaporation has occurred and delay the purchase of a new one. If a sealed no-maintenance battery has water evaporation or if it is affected by a charging system problem, nothing can be done to extend the life of the battery; it must be replaced.
Check your battery's health by measuring the specific gravity of the water within.
Recharging while you drive
If you have had your battery jumped, you will need to charge it with your car's charging system. Here are a few tips to quickly restore a battery.
Drive at a constant speed (highway driving) versus stop-and go (city driving). This will give the alternator an opportunity to charge more evenly.
Turn off all accessories (radio, air conditioner, etc.).
If possible, drive during the day. Even headlights use power. Having them off increases the amount of electricity going to the battery.
If a 12 Volt, typical lead-acid battery voltage is less than 9 volts when it is disconnected from any load, it is probably defective and should be replaced and not recharged.
A fully charged battery (disconnected from any load or charger) will have a voltage of about 12.9 Volts
A fully discharged battery (disconnected from load and charger) will have a voltage of about 11.4 Volts
This means that there is only a 1.5 Volt change from 100% charged to 100% discharged on a typical battery. Although the full charge and discharge voltage will vary by a few tenths of a volt, the 1.5 Volt swing from full to no charge is a good indication of the percentage charged the battery is.