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A majority of boats contain one or more batteries. At one time batteries were used for little more than starting the motor, maybe occasionally running a lamp or a small gauge. Today's batteries have greater demands placed upon them. Fish finders, GPS units, VHF radios, aerators and cassette players, all these units require battery power. Many of these devices are used when the engine is not running. This creates a drain on the battery's reserve which must be replaced.
All too often a battery dies an early death. As a general rule battery
manufacturers give marine batteries a shorter warranty period than their automotive counterparts, even though marine batteries are constructed with tougher materials. This is due to the fact that batteries in marine usage have a harsher life. They tend to go through more charge, discharge cycles. Physically they are vibrated and bounced around. Climb over a wave at 40 mph and your battery gets a jolt capable of breaking up its insides. Mostly the battery is ignored. It is not hard to imagine why batteries go bad before their time.
A battery is constructed from lead plates. Half of the plates are hooked to the positive post. In between every two positive plates is a negative plate all which are all connected to the negative post. Each plate is separated from the next by an insulator. A series of plates is arranged into a group called a cell and each cell produces 2.2 volts. Each cell sits in it's own bath of water mixed with sulphuric acid (electrolyte). When six cells are packaged together it becomes a 12 volt battery.
Battery plates are constructed with a soft form of lead paste. This type of material makes for an efficient battery. The lead is applied to a support structure to help hold it in place. The structure may be a specially constructed grid or may be ribs formed in the insulators separating the plates.
From the construction details you can imagine that the plates are subject to mechanical damage. Slamming, banging and vibrating a battery can cause bits of the plates to break loose and settle in the bottom of the battery case or it may cause a plate to break in two. The plate connectors are also subject to breakage.
Batteries can also suffer chemical damage. This occurs when the batteries are allowed to sit for a period of time in a discharged state. What will happen is the normally soft lead will start to chemically change into a hard form of lead, a process called sulphation. This reduces battery capacity and is often referred to as a weak battery. Sulphation can also take place when too much acid is put in the battery.
Batteries that are charged too fast or for too long tend to boil out fluid. The tops of the battery plates can become exposed to air and this causes a rapid sulphation in the exposed lead. The harden lead will crumble and fall off reducing the battery capacity. Adding water (distilled only!) will stop this problem. Do not add acid to a battery. This upsets the chemistry of the battery and causes more sulphation to take place.
It is fairly easy to help a battery give reliable performance over its expected life. First, it needs to be mounted securely in the boat. Trays and straps are made for this, cost only a few dollars and are very easy to install. If the battery is exposed to the elements, such as in a small aluminum boat, it needs to be mounted in a battery box and kept covered. When you use a tray you need to cover the terminals with rubber boots made for the purpose. This is a very important safety point. Anything conductive falling across the battery terminals will cause arcing and possible result in explosion.
When you service a battery, start with giving it a cleaning. Acids tend to coat the outer case and under certain conditions will partially discharge the battery. Battery cleaner in aerosol cans are available and they do a very good job. A bit of baking soda mixed with water will also work.
Next check the fluid level. Carefully pop off the caps and peek inside. Be careful. The acid does burn skin. The vapors are explosive. Fluid should cover the plates completely. If the level is low bring it up with distilled water and placed it on a charger for a short while. If no water was added the charge state of the battery needs to be checked. First, test the voltage. A "12 volt" battery is actually fully charged when it is at 13.2 volts, a reading above 12.5 volts is acceptable. If the voltage is low it needs to be topped off. Leaving a battery even slightly discharged will quicken sulphation.
It is recommended that you use a small charger and allow the battery to charge slowly. This will help to prevent internal battery damage from a large current passing through it. As the battery charges you might need to adjust the fluid levels. Do not let the plates become exposed to air.
After you have had the battery on the charger for a time the fluid will start to bubble. This is called gassing. It means the battery is getting near full charge (about 90% charged at the beginning of gassing). This increases as the battery charges further till all the cells are gassing freely. Heavy gassing indicates the battery is being over charged. Don't let this happen - the bubbles actually break chips of lead off the plates. If the battery gets hot it is being charged too hard. Under normal charging conditions they will get warm. A hot battery should be taken off of the charger and allowed to cool (check the fluid level!). If you have a continual problem with batteries getting hot your charger is putting out too much current.
Checking the bubbling is not quite a scientific way to tell if a battery is fully charged but if you don't have any other testers it will do. A better way is to use a hydrometer and a voltage meter. A fully charged battery will around 13.2 volts and a hydrometer will show a reading of 1.265 to 1.285. If the battery voltage is at 13 volts and the hydrometer reads high (above 1.30) there is too much acid in the battery. Try removing some of the fluid, replace it with distilled water and continue charging for a short period.
If you notice that the battery is gassing freely except for one or two cells, the battery may be going downhill if not already weak. This tends to happen when batteries have been charged with too high a current. It might be time to check your wallet to see how much faith you have in the battery.
When the battery is fully charged clean the case and return it to the boat. Hook up the wires and make sure you have good secure connections. Clean any terminals that need it. If they are badly damaged replace them or have them replaced by a mechanic. It is wise to avoid the wire wrapped around the post type connections. Have a proper terminal attached to the wire.
A battery that is not being used for a period of time will discharge on its own. This is true of all batteries, new or old. If nothing is done about this the battery can go bad. If you want to save the battery put it on a trickle charger overnight once a month or every other month. Another method would to be to get a maintenance charger and leave it on the battery all the time. All unused batteries loose that same amount of charge in a given time (the loss is somewhat mechanical) and these type of chargers have an output the same as the battery's natural loss.
It is important to keep a battery from freezing. A charged battery can take colder temps than a discharged one. If you have any concerns that your battery may freeze during the winter go ahead and store it in a protected area. It usually takes but a few minutes to unhook it. It also makes it easier to give it that occasional charge.
When working with batteries, do be cautious. Battery acid is a danger. It does burn skin. If gotten on clothing it will eat a hole in the material (usually shows up after the first laundering). Do protect your eyes and skin. Do not get acid on clothing. Charge batteries in well ventilated areas. Vapors from the battery can be explosive. I have only seen two batteries explode in fifteen years but both have taught me respect for the power that can be produced (the first one I saw almost made it 20 feet straight up - I think the tree branches stopped it from going higher). Read all precautions and instructions provided with chargers and test devices.
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