The LV is currently sitting at 3.17v right now, I've woken it up a few more times just to see what'd happen. For these tests the 7ah is still sitting installed as it should be, I simply tapped the LFP into its - screw and utilized the threaded post on the positive to attach it (there's a little threaded post under the red cover that I have a nut for). I haven't turned the key on, but if I turned on accessory, the DC/DC would supply 12.75v or so. Most of the LFP's power is in the 3.2v-3.4v range (temp dependent) so when it drops down to 12.6 or so at these temps, that's when the AGM starts to back it up if higher amperage is pulled. It's a much different story with my larger ones, I've got a 110ah unit I'm still working on that will let the truck pull 50 amps from while staying above 13v (this is the long-term battery for the truck though it's physically 10% larger than I need it to be to fit nicely), and the 280ah isn't phased by anything.
Yes, the LFP 'rules' are to prevent degradation. They can be discharged at 0f and charged around 25f to maintain their full lifetime which is 3-6,000 80% depth of discharge cycles before there's only 80% of rated capacity left. Then the cycle repeats of another 3-6000 cycles before 30ah>24ah becomes ~18ah. Even if my few below freezing recharges wipes out 90% of its life span, this thing should still have a decade of use here. These are LFP, not Li-ion. Big difference. When LFP dies it goes quietly into its goodnight. When li-ion dies it can turn into a ball of flames. Huge huge difference between these chemistries. I wouldn't use neither traditional NMC Li-ion or lithium polymer chemistries as they're fire hazards. LFP is a very safe chemistry.
I don't know how you would measure that. I suppose putting something 3+ inches tall on top of battery and seeing if hood closes.
I'm betting I missed something along the way, or maybe another thread. It seems you're running this in parallel with the small rear seat factory battery. Yes? Just adding in some capacity?
I've had this batt installed w/ out the aux batt in place in its modified battery box during warmer months. I'd removed it to do testing on the batt itself putting the factory batt back in (as in it was installed with lid and no way to know it was there w/out opening the aux batt box and seeing it). Because of low temps here recently, I decided to put it back in temporarily for testing with temps being in the teens (positive). The aux batt being present has virtually no bearing here due to its tiny size. I've read several papers on LFP charge / discharge at below freezing temps in ranges I see here, albeit rarely. Temps in the teens are maybe a few days a year, single digit temps can be counted on 1 hand/yr.
I have only read posts regarding the replacement of H7 sized AGM batteries for the PB, and of those posts, I have not heard a single low voltage complaint after replacing with a quality non-OEM product.
