Hi I've had my 2005 Prius for around a week now and I'm averaging 52mpg (UK gallon). I followed instructions on this forum for checking the 12V battery and found that it was a volt or so under the recommended. would this have much effect on my mpg? as far as i can tell the battery has never been changed since new. any advice is much appreciated!
52mpg is not bad for a new owner but a poor 12v battery will affect mpg, do not buy a new battery from the dealers as the correct fit batteries are readily available from motor shops at much better prices about £45- £50.
As long as you haven't recently attempted charging, the battery voltage for a healthy battery should be around 12.6 volt or higher. If you have charged it, just drive it for a bit, with the headlights on too, before checking voltage. A volt or two low (assume you're checking with a digital volt meter) is significant: 4 or 5 years is a good run for a battery. If you're on the orig. battery you've been lucky. It will leave you stranded soon: get it changed.
You folks in the UK are lucky, I hear that you can get the Optima D51 battery with Japanese terminals there.
There are many ways a 12 volt battery may fail. One of those ways really pulls down the fuel mileage. (single dead cell) Other ways to have an old battery fail may not effect MPG.
