Battery

February 21, 2023

Last weekend my car would not start.  Although I was perturbed, I had prepared for this probability.  When I was younger, I constantly locked my keys in the car, had flat tires or a dead battery, or was getting towed.  While my regular insurance says it will cover these events, I rarely use it and have a tow package from a national carrier, but they seem to take at least an hour to arrive.  I purchased a handheld charger unit just in case.  When I attached the small unit to the car it did not start.  I noticed it was not fully charged and thought that might be the culprit.  I hooked Melissa’s jumper cables to my car, and it fired right up.  I did the safe thing and took the car to our local battery dealer to have it checked.  The shop found the battery was low, but still good.  I remembered the AUX Battery light I had gotten earlier in the week.  The shop told me I needed to take the car to the dealer to have the auxiliary battery replaced.  That was the first time I knew my car had an auxiliary battery.

When I looked online, I found the Jeep Wrangler JL has the Electronic Start Stop System (ESS).  The idea is to save fuel by shutting the engine off automatically to prevent idling when the Jeep is sitting stopped.  The auxiliary battery keeps the accessories and computer alive when ESS stops the engine.  The dimensions for the battery are 5-3/4 inch (14-1/3 cm) x 5-7/8 inch (14-2/3 cm) x 3-7⁄16 inch (9-2/3 cm).  The battery weighs around 11.5 pounds (5.2 kg) and can produce 200 cold cranking amps (CCA).  The auxiliary battery is insufficient to provide cranking power to the starter motor and only keeps systems alive when the alternator is not making current.  While the average 12-volt car battery typically lasts three to five years, the auxiliary battery is smaller and has a lifespan of two to three years.  I guess I should feel lucky as I have had the vehicle for nearly 5 years.

While I did not know my vehicle used an auxiliary battery, I heard hybrid electric vehicles (HEV) and electric vehicles (EV) used an additional battery.  The difference between HEV and EV auxiliary battery systems and conventional vehicle systems is the method used to recharge the battery.  Instead of using an alternator to charge the auxiliary battery, HEVs and EVs are recharged by the HV battery using the inverter/converter.  Many HEVs do not use the 12-volt auxiliary battery for starting the gas powered engine or for the traction motor(s) which is charged by the traction battery.  While the auxiliary battery usually supports all 12-volt electrical systems on the vehicle, exceptions are the air conditioning and heating systems.  An auxiliary battery may also be used as a safety backup to support the main battery when required or to provide constant voltage for specific vehicle systems.  Many vehicles with ESS and ADAS (Advanced Driver-Assistance Systems) systems may also utilize an auxiliary battery alongside the main vehicle starter battery.  That is the case with my car.

THOUGHTS:  As a child I learned dinosaurs had a second brain.  The idea comes from an 1880’s cast of a Stegosaurus’ brain case.  Despite the massive size (5 to 10 tons), its brain was a little bigger than a walnut.  Scientists theorized the large, hollow space near the hip of the spinal cord contained a “second brain” to help control the back half of the animal.  Similar hollow spaces were later found in the rear of other sauropod dinosaurs and the myth of the second brain was born.  While the two brain myth persists, it is incorrect.  Birds are the closest living relatives of dinosaurs and have a similar space at the base of their spinal cord which stores energy-rich glycogen.  We do not know what the space is used for, but it is not a brain.  I was told my vehicle’s auxiliary battery was also in the rear of the vehicle, and that is also a myth.  I found an illustration of the placement showing the battery next to the larger 12-volt battery under the hood.  At least this battery does control the vehicles’ secondary functions.  Just because someone says it, and we all believe it, does not make it true.  Act for all.  Change is coming and it starts with you.