Troubles w/ 12v Battery/System - Puzzling - Please Help!!

I’ll try to be concise.


2006 with ~78k miles and smart key, new to me. The first night, after driving it home (~200 miles) and then to work, where it sat for a few hours, it started up without the speedo and related components, then refused to shut down at home. It seemed cut and dry: 12v battery issue.


I checked voltages from the MFD, and it seemed to support this. I was seeing around 11.9-12v and 13.9-14v. I didn’t document them exactly, because it seemed obvious. I charged at the battery directly @ 2A for several hours. It worked for a few days or so, then problems recur.


Battery voltages are pretty constant as stated above. But it consistently doesn’t work for a couple of days and only intermittently will give speedometer and gauges or shut down OK. Seems obvious, so I buy an Optima battery. Wanted to check Toyota battery date code first, but it’s way down there and I’m a single parent to a 4 yr old and 16 month old with no help. That’s why I’m working on this at 4AM.


Anyway, it’s been working like a champ for the past few days, but the battery seems on the verge, so I finally get up to change it this AM. Well, here’s the thing, I’ve removed it, and it is not only giving me 12.8v on a multimeter, but it appears to be a 2016 battery.


There is a purple sticker that has G16 on it and it is also marked 150216W, which, I think translates to manufactured in Feb 15, 2016 and sold or marked as July 2016. Am I assuming that correctly?


It is also a GS YUASA battery with Toyota TrueStart 84 month on it.


And finally, on my DieHard battery charger, it’s been charging since I started writing this. And now the green light is coming on to indicate that it is full. I was charging at 2A with “maintenance free deep cycle” selected, as it is AGM. I also tried “conventional low maintenance” and it shows all charged.


Luckily, I have other vehicles for transporting the kids, but I wish I could solve this now. Any ideas yet? Anyone have this issue?


I’m thinking my next step is to load the Toyota battery and the new Optima into my other vehicle, drop off the kids at daycare, then have AutoZone test my Toyota battery and return the unused Optima. God, I hope I’m not going to be out $200 for that thing!!


If the Toyota battery is bad, great!! Right?! Shouldn’t I be able to swap it out for free (or really cheap) at a dealership? It’s only about as old as my son - well under 2.


But what if the Toyota battery is good? What are the next troubleshooting steps?


As an aside, this makes me miss my first gen Insight. You could literally remove the hybrid battery, and it would still start using a $30 lawnmower battery under the hood. And it would get significantly better MPG than the Prius, still. But it was missing a lot of creature comforts... like a back seat, leather, smartkey, a useless MFD that isn’t built to last... ugh!


Thanks in advance for your help. My kids would high five you if they could!

 

Apparently I typed this earlier and it never posted....

Thank you so much for all of the detailed information! I have been reading various threads about it as I try and get some work done today.

I should be able to DIY the cluster. Probably have to get up at 4AM again though... ugh! I used to solder mod chips with the tiniest of connections and also used to build grid chargers, so I could probably handle the work. But with the complexity and obvious potential to screw up, I should probably have someone else do it. I have other vehicles to drive (although someone seems to have misplaced my keys since Halloween).

Does everyone do the same repair? It seems that there were a few different things that could be done. In other words, everyone is probably doing A or A & B, but some people might also be doing C or D, E and F. Does that make sense? Is there one standard, trusted vendor, (Texas Prius Battery Replacement), or should I consider different options? Should I stay away from others, such as the $99 ones on eBay?

Seems from what I read that Texas Prius Battery Replacement is probably the best, as they can program in the correct mileage and mail me a replacement unit, so I can swap it in and out in one action.

 

I'm a ways out from Tampa. I can do it myself. I've done a lot worse. Just finding the time... but I have backup transportation and it runs without it turning on anyway. Daycare is half a mile from home and work is only 5 miles anyway... I almost never pay for labor. But it's hard nowadays. Basically, things just don't get done...