For those of us who do mods like adding a 1kW inverter (for camping, running a microwave, rice cooker, or even pert of your home during a power outage), having the battery in the back is a gift. Otherwise you have to bring big cables through the firewall, figure out where to put the inverter, etc. You can see what I've done this way in the links below.
there was great joy when gen4 was announced with the 12v under the hood. most of us thought they would use an inexpensive common battery that fit a lot of cars, was larger so it didn't discharge so rapidly, wasn't as damaging if it did discharge, and didn't require the safety design for interior use. unfortunately, toyota in their wisdom decided to use another very uncommon, expensive battery, so the only difference i can see is that auto parts stores will install it for free, while they balk at the complexity of the hatch battery.
Gen 2 has a vented battery in trunk and yes the Toyota (Panasonic) ones are more expensive. Having said that I have had to replace 2 of these at 6 & 10 years, so they do last a long time. Also there are jumper terminals in the engine bay. I once did need jump ... from an electrician in a big truck ... he thought I was crazy when I rolled out some lightweight speaker wire for the jump start.
In your case, do you know what maximum current you draw out of the 12v with inverter on? What size 12V fuse dis you connect inline?
See my videos below. Briefly, you can safely draw 1kW but it's not really coming out of the 12V battery, but from the DC/DC inverter - and only when the car is on (the engine cycles on and off as needed). I use a 100A fuse. (To make sure my fuse blows before the 140A fuse built into the 12V battery's positive terminal.)
Not having to actually turnover an engine means these batteries see less abuse. They should last a long time. I thought there were jump points in the engine bay. Just been awhile since I looked under a Prius hood. Makes sense that is the case for any car with the battery mounted elsewhere.
There's some temperature-related reasons to not do that - for cold performance, lead acid does better than NiMH which does better than lithium-ion. Given that Toyota is still hanging on to NiMH in many of their hybrids specifically for the temperature reason, I don't see them switching to Li-ion for the 12 volt system. (For that matter, I'm surprised they're actually putting a Li-ion pack in the Gen 5 Prius AWD, and didn't just use a bipolar NiMH pack like they've recently debuted in some other models.) (Also, the Ioniq/Niro Hybrids do have a 12 volt battery, it's just a separate Li-ion sub-pack inside of the main HV pack's casing, and in some markets they instead had a conventional lead-acid 12 volt battery.)
How much of the market needs to concerned with temperatures below -20C/-4F? Using lead-acid there is an option, and some of those places require heaters for even them. Hyundai using a 12V Li-ion makes this market specific equipment approach easier to accomplish. Most of the hybrids with lead-acid were early released models. The global roll out was in Asia and Europe first. I don't know the details as to why, but they didn't get the L-ion at first. North America was the first market, but the others eventually got it. Most buyers only care that the Li-ion starter is good for the 'life' of the car, and that it can self jump start itself from the traction pack if need be. Further reduction of maintenance items was probably what some were hoping with the Prius. Toyota is still using NiMH because they make the most of past investments. The others use Li-ion because of availability and cost. NiMH is better in the cold, but how much of a difference has there been between hybrids in cold climates? I think the bipolar NiMH has limited manufacturing capacity at this time, and it likely is still more expensive than Li-ion. Is there any technical reason a bipolar Li-ion battery can't be made?
I've seen performance degradation - to the point of getting almost no energy flow to or from the HV battery after starting the engine, verified on Scangauge - on my Li-ion Gen 4 Prius as high as +20 °F/-7 °C. Presumably some of this is to protect the battery (charging a Li-ion below freezing is a bad idea, and it's not great to discharge it heavily below freezing), but it is a concern - you would basically have to have a battery heater on a Li-ion auxiliary battery to get it up to temperature quickly so you could recharge it for the next start. (Also that performance degradation is real fun when the engine computer's also limiting the engine to 3600 RPM due to the cold, and you have a freeway merge. ) I've seen the occasional claim that the bipolar NiMH option is cheaper, although the real advantage that Toyota is pushing is power density. Looks like it's a technology that already exists: https://onlinelibrary.wiley.com/doi/full/10.1002/advs.202001207 Not sure if there's something about NiMH that makes it easier, though - for instance, the substrate needed to do it on Li-ion could be a limiting factor for performance or something?
Yeah, charging at those temps is a concern. However, there are Li-ion chemistries that work at those temps. Toshiba claims safe charging down to -30C with their SCiB LTO batteries, and they are marketing starter batteries with them. The cost is higher, but not as onerous for a 12V as for an entire traction pack. SCiB™ Rechargeable battery | Toshiba Cheaper than the old NiMH, but Li-ion? Nickel is still more than lithium. If costs got close, the usable SOC range for long life of NiMH means you need more battery than a Li-ion of comparable output. With the announcement of improved Li-ion for the Crown and Prius, I was wondering if it meant Toyota is using bipolar.
For the average person, getting to a dead 12v in the rear hatch with a dead electronic release is very, very tough and not an intuitive process. Having had both and a DIY'er who's run power cables through the firewall for audio systems, I'd still rather have it under the hood.
That's more a math question than an experimental one. 1000 watts at 12 volts is 83 1/3 amps. If you figure the inverter is 90% efficient, it has to draw 1111 watts to give you 1000, so 93 amps. The DC/DC converter is rated (in a Gen 3, anyway) at 120 amps, and there's a 125 amp fuse (again in a Gen 3) shortly downstream of it. And of those 120 available amps, the car itself needs some (at least 30 and a lot more depending on what's being used). So Terrell's setup is pretty much right-sized to the car. Much of the time, the converter output will be slightly higher than 12 volts, more like 13.8, so the corresponding amp figures will be a little lower. But under highest loads, the converter's still doing its job as long as 12 volts are coming out.
I agree that getting the rear hatch open with no power is a PITA(I accidentally closed the hatch twice while having the car powered down to work on the dash wiring & air bag), but otherwise that should never be necessary. Just pop the hood, stick a charger or battery pack on the jump terminals, and either start the car or just pop the rear hatch.
I've had that happen to me. Very frustrating when you cannot open the rear hatch, because the 12V battery is dead. BUT the good news is the jumper panel under the hood allows very easy charging/starting.
In the Gen 3, there's a 140A fuse built into the positive side 12V battery clamp. When using the inverter, I make sure everything else is turned off (except of course, the car in Ready mode). I think perhaps Gen 2 is 120A? The output looks to be 14.5V (no load) on mine (assuming my inverter display is accurate).
The 12V battery can generate explosive hydrogen gas and is filled with hazardous sulphuric acid. In my opinion, something like that doesn't belong in the passenger compartment.
It looks like the Japanese car has a built-in 100V 1500W inverter, with a switch up front. I just now found this picture, which appears to be in the back hatch or rear seat area, which shows AC 120V and 1500W, which is what we use in the USA. That's great news! I wonder what trim level? It also appears that with the back seats folded down, the area is flat! That's also good news.
I’d say any market that has a proper winter season..so most of the northern states in the US, and pretty much all of Canada. Just like the extreme heat of the summer, it’s becoming much more commonplace to see extended periods of extreme cold in the winter. I can recall quite a few midwestern winter days in recent years where I checked the forecast in Antarctica and it was warmer there (days where -20 is the high) and these temps can easily hang on for over week. Usually this “polar vortex” only rolls through a couple times a season, but again, it’s a more common occurrence now.
