I have been concerned about the batteries in my gas Pacifica since I leased it. I put it on a trickle charger a couple of time a week. The ESS battery appears to be a motorcycle battery. If so, and if it is being used to start the engine repeatedly, IMO it is probably being used beyond its capability under the conditions of extreme heat that many of us expose these vehicles to. I wonder if a high quality battery of the same size might be a solution to the problem...an Odyssey battery for example. IMO the dealers will simply replace a defective battery with an identical battery thereby teeing up the owner for a similar failure later on. I think that the batteries in a modern, post 2000, vehicle should last three years and then be replaced on a schedule. I would like to hear from owners who have replaced the batteries with non OEM replacements.
The small battery is used run the AC fan (not compressor) and other miscellaneous functions when the engine is stopped by ESS, not to start the engine. From
"The small battery powers the majority of the electrical needs of the van when the engine shuts off, which reserves the larger cranking battery for engine starting. This is from the factory shop manual:
How does the ESS system function - simple overview:
- ESS shuts the engine off when the vehicle stops
- The vehicle has to be stopped for a pre-set time before the engine is switched off
- Then, it restarts when the driver releases the brake to move the vehicle
- The system senses brake pedal position and vehicle speed to determine that the vehicle is moving
- Powertrain calibration makes the decision when to shut off the engine and when to restart the engine again
- The ESS function is transparent to the driver
- When the engine stops, a smaller secondary battery keeps accessory features powered, like the fan, wipers, headlights, audio system, etc.
- A Dual Battery Control and Power Relay Control are used to smooth out voltage dips when the starter cranks the engine"
One of the things that can compromise the system is a faulty Intelligent Battery Sensor.