Function of the secondary battery in Start/Stop technology, FCA

Scott Shotton presented a case study on AesWave‘s blog, and explains the details of operation near the bottom of the post. Hope this is helpful, even if not from FCA itself… aeswave​.​com/blog/Parasitic…

That was very helpful; thank you for the link.

Second battery to to provide power to functions of the vehicle during a stop start event to preserve the main battery for restart.

Hey Phil! I know nothing about Chrysler of course, but on the short lived original Subaru Crosstrek hybrid, the little battery was for engine staring only and was charged by the belt driven alternator/starter. The other battery (a regular group 35) was used to power 12V systems and was charged with the DC-DC converter. When the little battery fails, you can see low voltage on the start battery…

It is not a hybrid the little battery is about the size of a powersports battery.

Thanks for the clarification, but the Subaru Crosstrek hybrid does have a similar system though. There are two 12V batteries and one “high voltage” battery (high voltage in quotes because it's only 100V). Because of the design, the high voltage battery can't crank the gas engine, so the starting battery does that job with a starter/alternator. The starting battery is a tiny battery with tiny…

Oh the Subaru first gen hybrid…. When the main battery starts dying ($180 installed), it leans on the start stop battery (950 installed); and if further ignored takes out the ISG (integrated starter generator).

On those vehicles, the small battery powers up all of the vehicle accessories only during an auto start event. The main battery is isolated to only power the starter. There’s also an isolation relay that controls which battery is connected.

I keep forgetting some manufacturers do this. When I was with Toyota we have one main battery and if the vehicle had heavy accessories the vehicle had a boost inverter to aid. I think we had only the Highlander and they have put it in the RAV4 and Camry by now. Granted it is not perfect and the main battery is almost $450 last I checked. I guess knowing how it fails and what the vehicle does…

Hello guys, Just my 1.012cents worth.. The Chrysler Pacifica is basically a rebranded R-Class Benz. I service a lot of Mercedes . The “Secondary” battery is there to maintain accessories that are equipped on certain vehicles to isolate power from the primary battery during start up and assist as backup during long or extended periods of ”Engine Off” accessory functions such as the “REST”…

The CS body or older Pacifica only has a single 12v battery, the current Pacifica after 17 has 2 batteries and is a FIAT based vehicle.