Has anyone tried replacing the 12 volt battery with a LiFePO4 12.8 V battery?

What I am trying to say is that "12.2 volts" is not a battery SOC. It is a bettery voltage.

 

So basically your nit pickin my use of SOC. You wanna be the first to take a set of Amp reading while 12 volt charging is happening by the Gen 4 and or 5 Prii, so we all can hone in the real 12 volt battery SOC, and I'll promise to never use SOC in a description of only the voltage reading again. Great job.

 

The 13.5 volt is pretty consistent, yes. As can be seen here when the battery was warming up


And when preheating (or A/C) was turned on (that 13.5V before the drive was 10 minutes long)


But when charging, the voltage does fluctuate, as can be seen below. It fluctuates around 12.8V.

 

It's probably like the Prime. The 100% of the traction battery for EV is actually from 15% to 85% of the traction battery. At 8.8kWh, that's 6.1kWh. Below 15% is reserved for the hybrid mode. Above 85% isn't used to, like you said, prevent battery degradation.

 

The voltage is important. LiFePo4 battries won't hit 100% charge and will begin to suffer sulfation unless they hit something like 14.8v during charging.

The guy who mentioned charging system voltage dropped great information. That means that adding any kind of lithium, even with a battery isolator, isn't going to work.

I almost installed that solution with a standard isolator. I see now that I'm going to need a different solution such as a DC to DC charger added between the regular supply of current, and the isolated lithium battery pack (I'm going to be powering an inverter) however this all definitely answers the question of if you can put a lithium batter into your prius as a starting battery.

Nope, you can't use a lithium starting battery. You'll mess it up and waste your investment.

You also definitely can't do it with LiFePo4, because those will take damage during every start since they're made for slow cycling, not fast discharge like lead acid.

AGM is ok in a Prius. Every time I buy a new 12v starter, that's exactly what comes up in retail matching systems like at Autozone. AGM isn't a true deep cycle battery, it's more or less a non-spillable improved version of lead acid that handles deep cycling better, but not as well as an actual deep cycle battery made for deep cycle applications like solar, running inverters, etc.

 

Where will the sulfur come from?

 

Damn diabolical question))