Last month, I replaced the 12v battery in my 2012 Prius with an OEM from Toyota. My mpg quickly improved from 30 mpg - 38 mpg. Recently, my mpg has dropped back down to 31-33 mpg (driving local, 2 miles each way to and from work) so I am concerned there's an issue with the 12v or the ignition/electrical system. Here are my readings using both the Prius Vehicle Signal Check mode and a multimeter: 1) Car off (left overnight) - 12.6v 2) Acc mode (power button once, no brake) - 12.6v 3) IG mode (power button twice, no brake) - 12.2v 4) IG mode + headlights on + max fan + front&rear defrosters - 11.2v 5) Engine on - 14.4v 6) After driving for 2-3 minutes - 13.5v Checking in various forums, it doesn't seem like any of these numbers are off expect maybe dropping to 13.5v after driving around for a few minutes. Is that normal or is it a sign there is an issue with the alternator? I would like to rule out any issues with the battery/alternator before moving on to other areas that might be causing the mpg drop. Gasoline has been winter mix this whole time so I don't think that's the issue. Thanks in advance for any insights / advice.
There is no alternator. The 12-volt charging supply comes from the DC-DC converter in the inverter with converter assembly; New Car Features (more info) says its output voltage can vary from 13.5 to 15.0 V. I don’t see anything abnormal here.
Check it with an electronic load tester, something like Solar BA9. If you can't swing the price, various retailers selling batteries will likely have a similar, pro-level tester, check it out for free. That said, it sounds like your battery is ok. Maybe low tire pressures, or dragging brakes. Check pressures, also feel all the wheels after a drive, see if any feel unusually warm, warmer than the others. How many miles on the car?
Given the readings that you got, there are subtle clues that the battery isn't being fully charged by your extremely short trips. And maybe it wasn't fully charged when installed either. A fully charged "new" AGM battery should read about 12.8 volts and that .3 difference is important. I suggest that you charge it overnight with a small charger and then do your readings again the FOLLOWING day. Given your stated usage pattern, you might need to connect a battery tender every few days to keep it from ever so slowly losing charge. Of course, there might be an entirely different reason for your loss of mileage.
Really short commutes , as @sam spade 2 says, are hard on mpg and the battery. I'd second @bisco too, an EGR circuit cleaning (including the intake manifold) is due. Are you second owner? Or your usage has dropped in recent years? If it's got 125K miles now, that took some steady driving.
I am the second owner. I bought the car used at 96K miles and at that point my MPG was about 44 highway / 40 local. Over 3 years and 30K miles it's dropped to 37/33 mpg
Two-mile trips. Ouch! Your poor car. That's brutal for any engine even if you do put the battery on a charger. I'm certain that that's why the gas mileage is so low, plus not having time to keep the battery fully charged. Is there any way you could go to a BEV or a PHEV? Either would be great in your situation.
I've been using a CTEK 4.3 for a few years now, no problems. It comes with a quick connect, which I installed at the 12 volt source in the underhood fuse box (See @NutzAboutBolts videos thread, pinned at top of 3rd gen maintenance forum). I connect it any day the car's not going to be used, let it run through a charging cycle and just leave it on till it does get use.
CTEK seems to make good stuff. Recommended by a LOT of owners. BUT.....do not confuse it with the CENTEK crap that Harbor Freight sells. Their chargers are junk. The little red multi-meter is pretty good though.
I wouldn't get the one I linked either. Apparently Amazon fed me the wrong model when I searched or else Schumacher changed the specs. Mine has a 2A trickle charge that works great. Edit to add: Every time I search for the SC1000 that I actually have, it feeds me this SC1359.
I couldn't see the attachment anyway. And....Jerry.....buddy....PLEASE don't refer to a smart charger as a "trickle" charge.
Not sure I would put much faith in a company that makes a mistake like that. Either it really IS just a dumb trickle charger OR it is mis-labeled. Either way, not a good sign.
