Retrofiting to run on battery only for short runs

[Jeri]

Another Prius owner (06) told me he was going to have his car retrofitted so that he could make the short daily runs on battery only. This he says will improve his mpg. Is this really possible? I also have four short runs per week and I know that this takes a toll in my mileage. Mine is an 05 if that makes a difference.

[JimboK]

Two retrofits come to mind, one expensive but effective, the other inexpensive but not effective for saving fuel through battery-only propulsion.

The first is an additional battery, likely with plug-in charging capability. Very pricey, likely not cost-effective (yet ... hopefully prices will drop), and technically difficult. It's not a job for a shadetree mechanic.

The second is an "EV switch" (as in Electric Vehicle switch). I have that, but I do not use it for sustained battery-only propulsion. Instead, I use it mainly to shut the engine off during its warmup cycle when it won't shut off spontaneously. See this for more.

[richard schumacher]

Because of the inefficiencies of energy conversion and battery charge/discharge, using the battery more usually reduces fuel economy, unless you manage use of the battery very closely (or unless you have a plug-in conversion; that costs $10,000 and will void your warranty).

Originally Posted by JimboK

I use [the EV switch] mainly to shut the engine off during its warmup cycle when it won't shut off spontaneously.

Uhh, doesn't that indicate that the engine and/or the catalytic converter have not warmed up enough? You may improve fuel economy but increase pollution.

[JimboK]

Originally Posted by richard schumacher

Uhh, doesn't that indicate that the engine and/or the catalytic converter have not warmed up enough? You may improve fuel economy but increase pollution.

The EV switch doesn't work during S1 when, as I understand it, the cat warmup occurs.

No one seems to have any explanation for some of the other warmup idiosyncracies, such as why it will shut down in S2 at a standstill but not while moving, or why in S3 it will shut down at speeds above 34 MPH but not below. Reducing emissions wouldn't seem to explain the logic of these design features. It seems to this simple mind that, once the cat is warmed, running the ICE pollutes more than not running it. I stand to be corrected and educated, of course, if someone has evidence to the contrary. Always looking to learn more about this remarkable car.