Is there a kit that simply tops up the traction battery?

Hi mlbex,
No, what you are asking for is not available. The Enginer PHEV system is the closest.

The reason there is not system is that it is not simple to do.

Also...
1. You can not get 100%SOC on the Prius HV Battery. The best you will do is 80%. Prius does this to improve the life of their HV battery.
2. You will not eliminate the warmup. The Prius warms up to heat the catylitic converter. This happens even with a full battery.
3. You will not get 5 miles out of the Prius HV battery. The best you will do is less than a mile.

The Prius must be "READY" to charge the HV battery. In ready with everything off the Prius draws 1.5a. Then you would need to add another 3a or more to have a reasonable charge. That is a killawatt or more of power. So a sugnificant power source would be required.

Thanks,
Dan

 

I believe the BMS+ system will do that. mrbigh is the expert on that one, although there has been another write-up thread titled something like "My Year with the BMS+ system" where you might read more about it. Basically the BMS+ would be setup, ready to accept more Prius battery packs, but would only have the original Prius battery pack to charge. I don't think it would be so expensive, but there are no installers to hook it up. (It might not be so difficult to hook up in this configuration though.)

But charging the battery pack is definitely not something to do without cautions, there have been people who have wrecked their Prius doing it.

 

Sounds like the Enginer kit would probably work for you. I drive around 4 miles to work and most of the time I can make it all the way there in EV mode without ever starting the engine.

Unfortunately, charging the Prius HV battery would likely have very little benefit. A typical Prius keeps the battery near the top of the SOC anyway. So there would usually be little capacity left to charge, and that would be an insignificant amount to really help fuel-economy.

One thing that might help you more is a block heater. I have been thinking about getting one. Even though I'm in Texas where it is usually warm, I have seen a dramatic drop in fuel economy due to warm-up time since Winter started. In fact, it has been around 22 degrees the last two mornings and I've had to run the engine to use the heater. As a result, I've gotten about 23 miles per gallon on my trip to work. The engine only reaches about 132 degrees F by the time I make it to work, which is actually lower than the usual operating temperature of 170 degrees F.

Another problem I've noticed is that I watch my battery voltage. Typically during the Summer I could drive for miles and miles in EV mode and my battery voltage would stay around 230 to 240 volts. Well, now that it is so cold, I'll see the voltage drop to about 180 volts within less than a mile of EV driving.

 

After recently installing a block heater in my Prius (in Wisconsin), I can say that it does improve fuel economy. The improvement is not as much as I'd hoped. Scangauge shows the water temp to be about 100-120F with ambient in the 10-20F range. After startup, it drops to about 80-100F and then rebounds. It increases the first 5-minute interval of fuel economy, but it is still less than a hot engine. I saw about 20 mpg before, now it's 30-35 mpg. The second 5-minute interval puts me around 50 mpg. In the cold of winter (WI winter) to can take 20 minutes to see optimum fuel efficiency.

 

Double posting

 

My BH while connected, keeps the block temperature at 87 deg at start-up, every single time since the last 5 years. I was suspecting some degradation through time but not.
Besides, I have it connected through a power thermostat so it will turn on at predetermine out door temperature.
After a night stand, on READY on, it drops the temperature a bit thanks to the coolant recirculation and rebounds also to a faster engine warm-up.
A PITA to install but was money very well invested.