|The MGA With An Attitude
BATTERY MAINTENANCE AND TESTING - BA-101
For sure you're attitude will take a beating if your car battery won't hold a charge or won't put out enough electrical current to start your car, or if the acid eats the paint off you car. BA-101 is a basic course in battery maintenance and testing. The first order of business is to keep your battery CLEAN. A dirty battery can conduct electrical current across the outside of the case and run the battery down while the car is parked. Acid on the outside of the battery can also corrode the cable connectors, eat paint and corrode the battery carrier tray. If you haven't figured it out yet, the battery (or batteries) in the MGA are (or should be) under a large cover behind the seats. If the convertible top is down and stowed you will have to put it up or at least pull it forward out of the way. The battery cover should have two slotted 1/4 turn fasteners, which you turn 1/4 turn anti-clockwise to release, then lift off the cover. If the battery is in the boot, utter three curses for the DPO, and watch out for taped up or frayed cables.
The best tools for cleaning a car battery are a stiff bristle brush, baking soda, and lots of water. Without removing the caps from the battery, wet the battery and sprinkle a little baking soda on it, then scrub it with the stiff brush. When the baking soda meets a little battery acid it will bubble and foam and fizz and make a general mess until it has neutralized all of the acid. Keep applying more baking soda and water until all bubbling stops. Be diligent at getting into all the corners around the terminal posts and near the filler caps and around and under the hold down clamps and the cable terminals. If the carrier tray is affected it's best to remove the battery to neutralize and clean the tray as well. When all signs of bubbling are gone, then rinse everything thoroughly with lots and lots of water, return the battery to the tray, and restore the installation of the hold down clamps and cable terminals if they were removed. Your battery thanks you, your car thanks you, and I thank you.
Next check and/or top off the fluid in the battery by adding plain water. (Find the discussion about "plain water" on the following page). Totally sealed batteries with non-removable caps are quite rare. Otherwise remove the top caps from the battery to check the fluid. Original type twin 6 volt batteries have three round caps which are either screw off of pull off. Newer 6 volt batteries might have a single rectangular pull off cap covering all three cells. Some 12 volt batteries have two flat rectangular caps covering three cells each. If these are flush with the top of the case you can use a small flat blade screwdriver to pry them up a little at a time from alternate sides until they pop off. Fill the cells until the fluid just touches the bottom of the tubular filler holes. DO NOT FILL COMPLETELY TO THE TOP, or it would bubble over in operation, and the acid will eat the paint and corrode the metal battery carrier and the battery cable clamps. Replace the caps on the battery, wipe dry with a disposable rag, and promptly dispose of the rag in case it might contain traces of acid, which you don't want to accidentally get on yourself, your clothes, or your car.
You will need a volt meter to measure the voltage at the battery (on the posts, not on the terminals). You will need to do this with the battery fully charged and at rest, and again when drawing a heavy current.
Measure the battery voltage. If it is less than 12.5 volts, put a battery charger on it until it comes up to full charge. Depending on the state of discharge and the capacity of the charger, this may take anywhere from 1 hour to 24 hours. If the battery will not produce at least 12.5 volts at the terminal posts after charging, it's a bad battery and needs to be replaced. The battery should have an open circuit voltage of about 12.6 volts when fully charged (6.3 volts for each 6 volt battery). If the battery voltage is still low after filling and charging, trade it in for a new battery.
You may need to do one more test on the battery. When drawing a high current from the battery the terminal voltage will drop due to internal electrical resistance. You could check this condition with an electronic battery tester or with a high current tester. If you do not have one of these instruments, you can draw a high current from the battery using the starter motor in the car. Disconnect the power supply wire from the ignition coil so the engine does not start. Or for the MGA you can just leave the ignition switch turned off when you crank the engine. Put a volt meter on the battery posts and verify at least 12.5 volts output. Then crank the engine (or try to) and check the terminal voltage at the battery while cranking. If the voltage drops to 9 or 10 volts, and the engine does not crank at all, then you may have a short to ground in the starter motor (likely where the input terminal passes through the end plate) which is pulling a very high current from the battery. If the engine does crank, but the battery voltage drops below 9 volts, the battery is bad or on its last legs and needs to be replaced. The battery should be able to maintain at least 10 volts for up to 20 seconds of cranking the starter with a cold engine. If it can't do that, you need a new battery.
If the battery can retain at least 10 volts when cranking, and the engine does crank but cranks slow, or at least the starter makes some noises, then the battery is okay, and you need to check the starter motor and all of the fat high current connecting cables. For that lesson refer to Slow Cranking Starter. If your battery runs down after some time in storage, refer to "Total Discharge is a no-no".
Thanks for your attention. Pick up your Battery Care diploma on the way out.