Electric Maintaince

Battery Care

When the weather gets messy and your yacht needs propeller assistance you want the engine to start. You can either crank start it (when did you last practice that?) or depend on your battery. So some battery care tips are not merely useful but essential for boating safety:

Checking

1. Visual inspection: Check electrolyte level at least once a month. If the battery is fully charged and still charging, water loss may increase. It is advisable that a new regulator be installed to normally prevent over-charging of the battery. Overcharging is indicated if the battery is bubbling vigorously.

2. Hydrometer test: Check the electrolyte level to see that it is above the plates in all cells. If it is below the plates, the test cannot be carried out until water is added and the battery charged to mix the water and residual acid in the battery. It is important to ensure that the plates do not remain exposed to air and allowed to dry and oxidize. The state of charge of each cell can be measured with a hydrometer to determine the specific gravity (S.G.) of the electrolyte (specific gravity is its weight compared to water).

Hydrometer Use

Draw the acid into the hydrometer so that the float is lifted free and not touching the top or bottom. The barrel must be held vertically and the eye must be level with the surface of the liquid. Disregard the curvature of the liquid against the glass (read from bottom of meniscus).

Generally the battery state of charge is as follows:
S.G. (@25°C) Volts State of Charge
1.260 6.32/12.65 100%
1.220 less than 6.22/12.45 75%
1.180 less than 6.10/12.20 50%
1.120 less than 6.00/12.00 Discharged
Cell temperature corrections should be applied if accurate readings are required. 0.004 points should be added or subtracted for each 5°C ± variation from 25°C.

3. Voltage Test: Voltage readings should be taken while the battery is neither charging nor discharging (nothing connected and turned on). Immediately after charging or discharging the battery voltage may not have stabilized. The voltage will settle down in about 30 minutes after charge or discharge is discontinued.

Electrolyte Level

Many batteries have markings on the cases to show the maximum and minimum advisable levels of the electrolyte. The lead plates in the battery must be submerged completely by the electrolyte, but there must also be a certain amount of headroom to allow the battery to gas without causing the electrolyte to spill out of the battery case.

Battery

1. Keep battery clean and dry - dampness lets electric current leak away.

2. Keep vent plugs in place to stop dirt falling into cells.

3. A thin coating of petroleum jelly helps prevent corrosion of terminals and connections.

4. For topping up cells, use either distilled water or clean rain water preferably collected in glass or plastic. Never top up the battery with anything other than distilled water or rainwater. Tip: A dehumidifier produces copious amounts of pure (distilled) water. Ask a friend with a dehumidifier for some of its water.

5. Make sure that the positive and negative plates inside the battery are covered with electrolyte at all times. Do not overfill.

6. Avoid adding water to a battery just prior to taking a S.G. reading as the reading will be misleading. If water is to be added, the battery should be charged for a while to mix it with the electrolyte thoroughly before the reading is taken.

Maintenance Schedule

Item to Check Frequency

1. Check S.G. of electrolyte 1 month
2. Check level of electrolyte. Top up if necessary 1 month
3. After boost charge check cell voltages. These should correspond to each other to within 0.05 volts 1-6 months
4. Check tightness of terminals and remove corrosion if necessary 6 months

Notes

DO NOT top up the battery cell with water when the battery is in a state of discharge. If the level of electrolyte is low, top up only to make sure that the plates are covered and no more. The fluid level rises with the level of charge, so if water is added when the battery is discharged, it may overflow on charging and lose electrolyte.

DO NOT use alligator clips or other sprung jaw methods as sparking often occurs when they are removed or attached, Hydrogen gas is generated by batteries under charge which is very explosive in the presence of air. Sparking can ignite it. The resulting explosion will not only destroy the battery but also injure the person holding the alligator clips with flying debris and battery acid.

DO NOT lift the battery by the lugs or terminals. Batteries need to be adequately supported from underneath.

DO NOT overcharge your battery to the point of heating the cells up. This will cause terminal damage. It is acceptable to charge to the point of the electrolyte bubbling. You may need to add water if the electrolyte level goes down.