Resurrecting a Dead Battery
The OEM battery that comes with the Miata is a sealed
absorbed glass mat (AGM) battery made by Panasonic as apposed
to the standard "wet cell" that is found in most other cars. Currently
they only come on new Miatas. You can't even buy a replacement AGM battery that
is just like if from a Mazda dealer. Dealers sell an old fashion wet cell.
The Mazda designers originally selected an AGM battery because it is lighter and won't leak fluids
in your trunk like a wet cell would.
These batteries have a very long life. We have heard of people who have
batteries that are 8+ years old and still going strong.
There are two draw backs to this type of battery.
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1) Draining them all the way down can destroy them. So it is important that
for storage the battery is disconnected or better yet, put on a charger that will
"float" the charge of the battery.
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2) If a light is left on and you discover a nearly dead battery, it will
not take a quick charge. Unlike wet cells that can take a jump and be fine. You
can jump a AGM to get it started, drive it 60 miles, turn off the engine and not
have enough power to start the engine.
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However - it is easy to breath new life into a seemingly dead AGM
battery. You do it with a slow, long charge. 1/2 to 1 amp for 24 to 48 hours
and in most cases your AGM battery will be like new.
Your can get a small 1/2 to 1 amp charger at just about any
auto parts store that will do the trick. The may be referred to as a motorcycle
battery charger.
WARNING - do not leave these chargers connected longer than 48
hours. These cheap chargers do not float the battery or switch off when the
battery is fully charged. As a result, they can cause a battery to explode. If
you are looking for a charger that can be left attached to an AGM battery (or
any battery for that matter) for
longer periods of time and will float the charge, we offer the WestCo
battery
charger.
Checking a Charged Battery
Once you have charged the battery, use a volt meter to check its
voltage. It should be up around 13+ volts. Wait 30 minutes and check it
again. If the voltage has dropped to near 12 volts or less, it is
probably time to get a new battery. The battery is either old or has
been damaged from being discharged.
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