Preemptively replace 12V battery?

When my original battery started giving me signs of going bad I didn't hesitate and just replaced it. I don't remember the details but things weren't working like they should especially at start up. The car always started though.
Have other people have a similar warning?

 

I have a 2011 and replaced the 12V battery it with a "Optima Batteries 8171-767 (DS46B24R) YellowTop Prius Battery" in Dec 2015 which was almost exactly a 5 year life. When the original battery failed, the little Li-ion jump starter pack I have (WEEGO 44 Jump Starter) wouldn't work because the 12V battery must have dropped below whatever the WEEGO's minimum cutoff voltage is, so the jump starter wouldn't feed power to the car. I was stuck.

 

Just for testing, I am able to start a V6 engine using just the jnc in place the car’s 12v 10 times consecutively.

Go big or go home.

 

Keep in mind that in Prius 12v auxiliary battery is not the one that starts the gasoline engine. It’s the hybrid traction battery that “crank”s the engine via motor-generator. So you can’t diretly apply conventional car battery wisdoms in cold-weather.

Having said this, drained out 12v aux battery will make the car fail to “start”, not because it won’t crank the engine, but because it won’t power up the computer.

 

That's debatable. The 12 volt battery may not crank the engine, but it's health is still assessable by testers that read it's cold cranking amps (or cranking amps, or a few other units). There's a new generation of testers (Solar BA5 for example) that do that. They're around $50.

A typical new battery in good health will have CCA significantly higher than it's rating. When CCA drops below it's rating, it's time to replace. The new testers will typically give a verdict, either pass, recharge and retest, or fail.

 

Should you preemptively replace something that hasn't reached total failure?

Reminds me of a quote I just made up from Chief Joseph.

" We use everything up here"- CJ.

Or maybe that quote was from Pennywise? The Clown from "IT"?

Actually if cost isn't an issue, I'd avoid the possible trouble of being stranded and just replace. That's a long run on an original battery, and IMO with a Prius, the functionality of the 12 volt, is of slightly higher importance than a regular vehicle.

 

CCA is a poor measure of Prius aux battery performance. In fact, it’s a meaningless metric because Prius is never going to draw huge amount of current in short duration from aux battery.

What’s important is how well the battery keeps its charge. This is why Prius aux battery is deep-cycle AGM type. Expensive, but it should last very long. Not surprising at all OP doesn’t have issue after 8 years. And it makes sense dealership gives whopping 84 month warranty. So I wouldn’t replace a working deep-cycle AGM battery just because measured CCA number drops below ‘spec’.

 

Up to 3rd gen the battery is in the passenger cabin, and AGM. 4th gen is under the hood, and conventional.

 

Which is shame because since 4th gen you have to pay more for worse part more frequently. Not many things known about gen4 345LN1-MF aux 12v battery which you can only get from dealership for $$$$

 

Yes...and $200 installed at the Dealership with an 84 month is a very good price.