Am I able to charge the auxillary battery by turning the car on and leaving it on Park for 15 mins? I've been garaging the Prius for 5 weeks and plan to continue garaging for possibly another 5 weeks. Last week, I turned on the car and kept it on park, blipped the gas pedal to force the ICE to start, and left it sit for 15 mins. But once the engine warmed after about 5 mins, the ICE shuts off for the remaining 10 mins. I have a 2 car tandem garage with the Prius in the back so I'd rather not take it out for a quick drive if I don't have to.
It does not matter whether the ICE runs. The auxiliary battery is being charged whenever the READY light is on. Power to charge the auxiliary battery will be taken from the traction battery, which itself will be kept charged by the car starting and stopping the ICE as needed. -Chap
Toyota’s service bulletins suggest a 30-minute run time, but yes, this is the preferred procedure. See T-SB-0043-16, “Maintenance for HV & Auxiliary Batteries,” published May 18, 2016, and T-SB-0045-16, “Long-Term Vehicle Storage Guidelines,” published May 19, 2016. It’s best to do it, too—according to the Repair Manual, the Hybrid Vehicle Control ECU keeps track of the number of times the vehicle has gone more than 60 days (1440 hours) without being powered on, along with the mileage and time for the last three such events. This information is included in the Hybrid Control Data List, which can be retrieved using a Toyota Techstream diagnostic system.
If you wish to make sure your 12v auxiliary battery remains fully charged without starting the Prius, get what is known as a battery maintainer. These are small low current chargers which do not continue to trickle charge when the battery voltage reaches a full charge. I’ve used these with equipment l wanted to avoid removing the battery during storage and keep them charged and ready, but not overcharged.
I use the "Battery Tender". It's intended for ATVs and motorcycles but works just fine on Pearl S. MUCH less expensive than buying gasoline and filling the garage with CO! You can connect it in various ways directly to the battery. Easy with the G4, a little harder with the GIII but still easy (boost point).
+1 ALL automotive parts stores, motorcycle shops, battery stores and big box retailers carry automatic battery maintenance chargers. Typically $30 or a bit less.
