Dead battery after 2.5 weeks

True, the US is actually on the metric system (the inch is legally defined as 25.4 mm, and the second is an SI unit), so the problem must be with those old Imperial seconds.

 

Jayman: Since replacing my 12v Aux. Battery, now over a month of same, same driving (no fancy hypermiling for this leadfoot!), my mileage has increased from approx. 36-38mpg to 43 - 44mpg. I plug the puppy into my BMW Battery Minder overnight and
S H A Z A A M, AWESOME MILEAGE (in comparison).

FYI, I drive approx. 15 miles round trip each morning to drop my kids off at school then back to my office. Ambient winter night temps are in the high 20 to low 30 degree (F) and days are in the high 30's and low 40's, so I use the heater, defroster, lights, the whole shebang.
My guess is that due to the shortness of time that I drive during the day didn't allow sufficient time for the 12v Aux Battery to recharge, causing it to get weaker and weaker over time... Not to mention the average 80 -100 degree Fahrenheit days in the summer and 60 + degree F nights in the summer. A Perfect Storm for really messing up the 12v Aux BATT.

DID I MENTION THAT I'M HAPPIER THAN A Chocaholic at a Candy Convention!!!
:cheer2:

Go Prius!

Thanks again to all!

Ken

 

Well, the honeymoon didn't last more than 4 weeks and my once stellar mileage has decline from approx. 43mpg back down to 38- 40mpg with similar ambient temps, same gas, same driving loops & same Battery Tender topping off the Aux. battery. I don't know what to think now!!! I was so pleased with the momentus increase in mpg from, what I inferred, was the replacement of the Aux/Starting Battery.

Anybody care to venture a guess as to why the mileage peaked so strongly after I replaced the Aux/Starter Batt???

Thanks, Ken

 

How are you measuring mpg? Are you logging odometer miles driven and gallons purchased? Or are you relying on the MFD display?

If the latter, then note that the MFD display can change over time as more data is accumulated by the complex system that drives that readout. This is reset when the 12V battery is disconnected.

 

Ken

Am unsure why. I've never noticed any difference using a Battery minder on any of my equipment. That is, not any difference in fuel economy.

For the rest of the equipment, the starter cranks much more strongly than before, and the equipment is much easier to start up

jay

 

Would a 10 day period of no driving hurt the 12V battery at all? Thanks!

 

With a new 12v battery in good condition and fully charged, 10 days should not cause a problem. Just shut off the system to unlock the car without pressing buttons (if you have it) as it does put a noticeable drain when the car is not being used. There is a button under the steering column that turns this function on/off.

Most of the discussion here is about long-term maintenance of the little 12v battery and a "Battery Minder" or "Battery Tender" does a good job of maintaining both the state-of-charge (SOC) and prevent/reduce the level of sulfate on the battery plates which is a major cause of failure in lead-acid batteries. One of these units is a good idea if either you are going to leave your car unused for longer periods or tend to do a lot of short trips (the Prius built-in charging system does not rapidly charge the 12v battery).

There is a simple procedure to test the health of your 12v battery. I have documented it in several of these discussions. You can see the procedure at:
Checking 12v Battery Health - Hybrid Car Forums
It is also documented at
http://www.elearnaid.com/12vo1topraub.html
which sells high quality replacement batteries for the Prius.