You can always put a heat pad in your battery box and insulate the box on the outside. Heat pads for seedling trays are commonly available, the better ones being waterproof and contain thermostats. For low voltage applications, the aftermarket car seat pads work well. Here in central Maine, I have 2 packs of Ternary cells subject to ambient temps, BMS protected and heated. Have used those for 5 years now without noticeable degradation. Just keep them above freezing. John M
"Money doesn't talk, it swears"--Bob Dylan Feb 25, 2026, 6:38 AM by [email protected]: > LFP sounds much more dangerous than I had been led to believe. I had been > planning to put a used Calb LFP house backup battery in the insulated > crawlspace under the airlock entryway. However the floor above the cells is > not airtight possibly gassing the escapees. I could just get another 8 golf > cart batteries to replace the old ones there that came from my first EV. I > had hoped to soon avoid crawling in there with a watering can. Connecticut > climate spends a lot of time below freezing, do you have more info about > charging LFP cells at or below freezing ? possibly slowly ? Is water > involved internally or do other chemicals have the same freezing point ? > My first EV (a '93 escort electricar) now has a Trimetal Li battery giving a > 30 mi range when above freezing and the '98 Solectria now has used coda LFP > batteries. Both have Orion BMS. > I am working on assembling 2 ea 72AH 12V LFP batteries to replace the lead > batteries for lighting. > Phil Dooley > On Tuesday, February 24, 2026 at 01:33:31 PM EST, (-Phil-) via EV > <[email protected]> wrote: > > To be clear LFP is a shortened abbreviation of LiFePO₄. > > Yes, That was my conclusion too. I have earlier video on it with more > details: https://www.youtube.com/watch?v=i27lApNWkyA (Note: This was made > 2 years ago before Tesla introduced the LFP version they are rolling out > now) > > Indeed, Tesla is now using LFP in some models for the "12v" system. LFP > is "safer" than ternary; No doubt, and more tolerant of abuse. If you are > building any kind of home backup or battery storage that will be in or near > your house, it's my opinion you should stick to LFP. Those cells can still > go into thermal runaway internally, but it usually doesn't spread to > adjacent cells. (USUALLY!) > > HOWEVER, LFP can still have nasty failure modes that emit huge volumes > (many orders of magnitude of the cell volume) of toxic gases that can > easily kill you and/or cause an explosion if they are inside your house. > So a large pack in your attached garage could easily kill you in your > sleep even if just one large format cell goes off! It should be in a > sealed enclosure with a vent to the outside. I've seen dryer vents used > for this with the little metal flap, so it stays closed unless there is > overpressure in the enclosure and then safely vents outside. Another > technique used is a foil seal. You see this on the top of many large LFP > cells. The foil will burst and allow venting, but ensures the cell stays > sealed in normal operation. Since you cannot charge these cells below > freezing, and they have a longer life if kept cool (i.e. They prefer to > live in the same temperatures we do), it's tempting to install them inside. > > I personally have a ~9kWh LFP battery in my house using 16 of the Calb > 180Ah cells in a 16S configuration. (~48V) It's in an air-sealed enclosure > with a vent fan that pulling air from outside through a filter and venting > out the top to a vent stack on the roof. I live in CA where I enjoy mild > temperatures, so the pack stays pretty comfortable. The fan is on a > thermostat set for 80°F and this is located at the top near where the fan > is. I specifically chose a brushless fan and solid state thermostat to > ensure there's no chance of ignition. This fan/thermostat arrangement > stops the air from getting too cold in the winter. My BMS keeps the cell > voltages from ever exceeding 3.4v and pack at or under 54v which is > conservative. This reduces danger somewhat and greatly extends the life of > the pack with only marginal reduction of capacity. I have a monitor on > the BMS that will send me a text if it ever goes too far off track, here's > the current state: > Overall pack: 54.0 V > Highest Cell: 3.384 V (02) > Lowest Cell: 3.375 V (10) > Cell Delta: 0.009 V > Battery Temp: 28 °C > > Note that regardless of cell quality, you should always expect an internal > cell failure, it's rare, but does happen. You should build your battery > system as I did, with this failure in mind! > > Here's a copy/paste from an LFP safety analysis: > "When a lithium iron phosphate (LFP or LiFePO₄) cell undergoes internal > failure (e.g., due to an internal short circuit) or is externally shorted, > it can lead to rapid heating, potentially triggering thermal runaway. This > process causes the cell to vent gases through its safety valve or rupture > points. These gases arise primarily from the decomposition of the organic > electrolyte (e.g., carbonates like ethylene carbonate), breakdown of the > solid electrolyte interphase (SEI) layer, and other internal reactions. > The emitted gases include both flammable and toxic components, posing risks > of fire, explosion (if accumulated gases reach ignition conditions in a > confined space), and health hazards from inhalation. > > Main Dangerous Gases Emitted: > > 1. Hydrogen (H₂): Often the most abundant flammable gas (frequently 30–55% > or more of the total vent gas volume, depending on conditions like state of > charge). Highly flammable and explosive when mixed with air; contributes > significantly to explosion risks. > > 2. Carbon monoxide (CO): Toxic and flammable (typically 8–28% range in > studies). Colorless, odorless gas that causes asphyxiation by binding to > hemoglobin; a major toxicity concern. > > 3. Carbon dioxide (CO₂): Non-flammable but can displace oxygen and > contribute to asphyxiation in high concentrations (often 15–36%). > > 4. Hydrocarbons (e.g., methane CH₄, ethylene C₂H₄, ethane C₂H₆, propylene > C₃H₆): Flammable and present in smaller but significant amounts (combined > often 5–15%). These lower the ignition energy and widen the flammability > range of the gas mixture. > > 5. Hydrogen fluoride (HF): Extremely toxic and corrosive gas (produced from > decomposition of the LiPF₆ salt in the electrolyte and fluorinated > binders). Forms hydrofluoric acid in moist air or when water is applied > (e.g., during firefighting); causes severe respiratory damage, skin burns, > and systemic toxicity even at low concentrations. LFP cells can produce > notable amounts of HF, sometimes more than other chemistries under certain > conditions." > > On Tue, Feb 24, 2026 at 7:55 AM Mark Hanson via EV <[email protected]> > wrote: > >> Hi Phil etc >> That’s very interesting that just normal charging ternary NMC cells that >> are dead at/below 2V per cell can cause a fire due to dendrite growth >> shorting out the plates. >> Your video showed Tesla using these cells in their 12v aux batteries on >> new EVs. Sounds like Tesla screwed up and should use LFP cells for 12v >> battery replacements like everyone else >> Do LFP batteries have the same problem if a dead cell <2V per cell is >> normally charged? I’m sure I’ve done this in the past with LiFePo4 cells >> without thinking about it (mostly small battlebots). Don’t recall running >> into this when I used to convert EVs using Calb or Thundersky LFP cells >> (since EVs didn’t sit to long without being charged) >> Stay Charged, >> Mark >> Sent from my iPhone >> _______________________________________________ >> Address messages to [email protected] >> No other addresses in TO and CC fields >> HELP: http://www.evdl.org/help/ >> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20260224/a9cb8b19/attachment.htm> > _______________________________________________ > Address messages to [email protected] > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20260225/3ddc3a19/attachment.htm> > _______________________________________________ > Address messages to [email protected] > No other addresses in TO and CC fields > HELP: http://www.evdl.org/help/ > _______________________________________________ Address messages to [email protected] No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
