[Isaac Zachary]

I need a 12V battery for the 2006 Prius. My thoughts are either go with a battery from Toyota, or I'd like to try lithium ferrous phosphate (LFP, AKA: LiFePO4).

I found a 40Ah one from a brand named Winston that looks to be very similar in size to the Prius battery. However, one of my concerns is cold weather. With Lead Acid (LA) you don't want to let the battery drain or it can freeze and even rupture. But since a car ususally will keep the battery topped off, this may not be a problem. LFP's, though, usually are damaged from cold weather, mainly when charged (discharging might not affect them in freezing weather). But Winston advertises they can work in -40 °F (-40 °C) weather without damage by means of a special chemistry. And we sometimes see weather down to -40 °F (-40 °C) around here on occasion, although not as often as in the past. I am contemplating getting a battery warmer too, just because. Also, being more inside the cabin, as opposed to being under a hood, seems like a better place to keep it above freezing during a sunny day, right? Or am I wrong?

Am I right about dimmensions too?
OEM:
220mm x 235mm x 127mm

Winston:
225mm x 208mm x 125mm

The Winston is also about $239, before tax and shipping. I'm sure there are cheaper options out there, but this is the only LFP advertised to work in the cold. Any thoughts on if I'd just be better off with an LA?

One reason I like the idea of LFP is I'm also into amateur radio. If I get a radio into this car, having more usable Ah's would be important. This is also my second car, and depending on how it goes, I might get an LFP for the Avalon hybrid, which does have a 100W HF/VHF/UHF transceiver installed. LFP also keeps the voltage closer to 13.8V, the perfect voltage for a typical transceiver, and it can do that without the aid of potentially noisy voltage converters. This is why LTO wouldn't seem like a good alternative.