Bad 12v or just normal

Battery | 2008 Toyota Prius 4 Cylinders B 1.5L Gas/Elec DOHC
| AutoZone.com


That's the "yellow top" that a lot of PC member's recommend. You can get that a little cheaper online here

Optima DS46B24R Optima battery direct fit replacement for Prius 2004 + & Plug-in Prius with Instructions

 

Buy it at Autozone online and then pick it up at the store. $169. Reports of some low charged new batteries. Bring a voltmeter and check it at the counter before you leave. Should be at least 12.8 at the counter.
Either way its a good idea to charge it when you get home.

Mine was ok when I picked it up. Its a drop in.

Since you will have the back apart take the spare tire out too and check for any water leak damage. Rust. If any water got in the trunk you will see rust under the spare tire. Clean the area under the battery good too.
Sand down the mating area for the battery ground lead at the body and the ground connector. Just reveal fresh metal. Grease the terminals up good with syn grease and the sanded area.

 

Can the 12V battery cause a sudden drop (47-48mpg to 40-41mpg) in a matter of a week or so? I'm trying to source why our mpgs have dropped suddenly. Weather has been pretty consistent, and only other change has been new tires. I'm hoping the tires we installed are not causing this major of a drop though. Tested my voltage again tonight and got:

Accessory Mode 11.8
Ign ON Mode 11.6
Ready Mode 14.1

 

In reference to your tires.

Please post the size of your tires, the brand name of them, and also the model of the tires. Also, is your Prius a touring or a non touring.

FYI, your voltages are low (weak) on your battery.

FYI, tires do play a roll in overall MPG. The Prius is fitted with LRR tires from the factory. Not all tires are LRR tires.

 

The tires we were replacing were stock size (185/65/R15) Goodyear Assurance Fuel Savers. We replaced them with same size Dunlop Signature II tires. Air pressures set at 40F/38R. 2005 Prius, Package #4, 114k, all service up to date.

 

It appears that the tires you purchased are not LRR tires. This will contribute to lower overall MPG.

If you can, you might consider exchanging the tires for a LRR tire.

F8L posted a very good list of LRR tires that you can read through.

Low Rolling Resistance replacement tires: Current List | PriusChat

You can see here that the tires you purchased are plainly marked non LRR tires.


Dunlop Signature - 185/65R15 88H BSW - All Season Tire - Automotive - Tires - Car Tires

 

Would LRR tires make that large of a difference?