I'm wondering if anybody has disconnected the 12v battery while the Prime is plugged in to find out if the 12v system remains powered.
I don't think so, but it might if it's actively charging the traction battery when you disconnect the 12v. My PiP, at least, does a trickle charge to the 12v while charging the traction battery. But I think it's more likely to just shut everything off. The easy way, if you want to spend a few bucks (not a lot) is to get one of those gizmos that you plug into the 12v outlet in your car and it connects to a 12v battery. If your computer is on a UPS, that's usually a convenient place to grab a 12v battery out of for this sort of thing. Or the cheap way is just to connect the UPS battery directly to the cables, but it's more cumbersome. Either way, be careful to not let the positive battery cable hit any metal part of your car when you remove it from the old battery or connect it to the new one because it'll be live. Best to wrap the clamp in plastic while you're R&R-ing the battery. I've never bothered with it since it's not that hard for me to get my settings back where I want them.
I'm not real worried about the settings, but I don't want to lose data like ev miles, etc. Since I don't know what is retained and what is lost, I'm cautious.
I seem to remember some threads around here that talk about that data and if it's retained, but I don't recall the bottom line since I'm still just dreaming about a Gen 4.
I use one of these: Laid in the driver's side footwell, with one of these, a purpose-built memory-saver cable with indicator light: Running from the jump pack (12 volt outlet circled), to the OBD port. The cable's OBD connector only has the 12 volt pins. Works good. In the past I've hooked a 0.5 amp trickle charger at the battery, clamped to the positive cable and ground. That also worked ok.
Thanks guys. I'll probably go the OBDII route if and when I change the battery. I'm just really nervous about Toyota using an aftermarket battery as an excuse to claim I "broke" the car somehow. I just have to decide if I want to try and fix the issue myself and let Toyota off the hook in the interest of just having the darn thing work (hoping the battery fixes it), or if I want the stress of pushing them through arbitration and potentially other legal action to force them to make a repair they are so reluctant to make. Just out of curiosity's sake, though, I still wonder if the charger will keep the 12v system alive.
I would suggest bringing home the replacement battery, installing it, and then driving the car for a day or so to see if that actually fixes the problem before taking the OEM battery in for the core charge refund.
Admittedly, I’m not 100% sure I understand your question, but FWIW, this awesome video: reports that charging the traction battery also charges the 12V battery, as I recall.
Starting around 26:30 minutes he discusses just how compressed the pack is. When the ends are freed the length increases by around 2". And it was only with great difficulty and a pair of pipe clamps that he was able to get it back together. Doesn't bode well for DIY cell swaps? Or at least something to keep in mind. Addendum: he mentions near the end that there's a warning in the Owner's Manual, to not carry in the hatch area liquids that could spill. Maybe there should be a decal to that affect, on the the rear seatback?
I just wondered if charging the Prime would keep the computers powered with 12v while the auxiliary battery was disconnected and replace with another. However, after watching an educational video about testing the 12v charging system, I don't think the battery is the issue. I think the issue is voltage loss between the fuse box and the outlet which may not be due to the wire gauge.
I think you will get a fault code and possibly a shut down of charging if you disconnect/open circuit the 12v battery. According to Prof.Kelly there are sensors monitoring the battery's health and that these are on a LIN bus. LIN is like the CAN bus we can read with the scan gauge or Torque app but LIN is usually connected to a specific computer controller. Hot swap? Maybe if both batteries had the same voltage and were connected with jumpers to put them in parallel... Sorry I don't have one to play with yet to know for sure.
Very informative video. I have an Optima battery in my 2010 Prius & hope to get many years of use. I am retired from the US Post Office & had Optima batteries in our Postal Vehicles. Many times I saw Postal Trucks with 10 year old Optima batteries still going strong. You consider how many times a day a Postal Vehicle has to start - sometimes 200 times a day on certain routes - I think an Optima battery has to be a prime chose for a replacement battery. It does cost more than a regular battery, but in the long haul would be well worth the extra cost.
