Fire dangers of a fully charged LifePo4 12v 100ah battery in home and only used for emergencies?

[rv888]

I have Goal Zero Yetis 1000X & 500x (plus several other smaller power banks) with GZ's Boulder 100 Solar case and some other 100 watt solar panels I've used for camping. I mainly use all of this at home for emergency power outages. I live a big building in a city and cannot attach anything to the building outside, but do hang things from windows or off my balcony. This has all been enough for me in the past.

We recently had a major outage for over 24 hours localized to just a few blocks around me, but I had to continue to try and work from home through out it. My setup was starting to run out of power towards the end so I decided that I'd like to extend it with an extra 12v battery. I looked into the GZ link and expansion setup, but decided against it and purchase a 12v 100ah LifePo4 battery to chain manually only when needed.

I've been trying to learn as much as possible about LifePo4 batteries and have seen a lot about the fire risk dangers. I've read lots of discussion on the voltage to use for "storing" them for months and also not having them fully charged unless you plan to use them right away, etc. Not sure if what I am doing would be considered storage since it would just be sitting in my house all the time until needed. But when that is, I can't say for certain until the power goes out.

In a situation like mine, where I won't be using this that often (hopefully anyway), just want it to be ready and available if the power goes out, at what level should I keep the battery charged to be safe (from fire dangers, etc)? I guess I'm not fully understanding the level of danger of having a fully charged 12v 100ah LifePo4 battery at home in room temperature and waiting for it to be needed.

For reference, I intend to chain it exactly like Todd Parker's video with my GZs. So when my power goes out, I'd attach LifePo4 battery to GZ for additional power.

Chaining lithium batteries to a Goal Zero Yeti: DIY Tank expansion for Battle Born LiFePO4 batteries

I ended up choosing the same battery he uses in the video, though that wasn't why. I looked at lots of others including cheaper ones, but ultimately chose them mainly because they are a local company to me.

ExpertPower 12V 100Ah Lithium LiFePO4 Deep Cycle Rechargeable Battery

Thought maybe you all here could help me.

Can I keep the battery safely fully charged as an at home standby power source?

Thanks!

 

[ernie314]

LiFePo4 batteries are considered to be fire safe because they have a very stable chemistry and a very low rate of thermal runaway, which is a condition where the temperature of the battery increases rapidly, potentially leading to a fire.

Here at around 5:10 you can see that puncturing a LiFePo4 battery does not cause a fire:

Having said that. If you puncture a battery and add some sparks from an external source, you can ignite the electrolyte:

 

[mikefitz]

I would be much more worried about the NMC cells in the Goal Zero Yeti, these are known as a fire risk.

There may be a slight degradation in capacity by keeping a LiFePO4 in a fully charged state, there are conflicting reports on this issue. I don't think there will be a serious problem , the very small loading of the BMS and low self discharge will gradually lower the SOC, perhaps needing a top up charge every 6 months.
I would not advice leaving the battery continuously connected to a charger.

Keeping the LiFePO4 battery fully charged is very safe if;
Its disconnected from everything, with the battery terminals protected against accidental shorts, and the battery protected against mechanical damage.

Once you connect anything to the battery the risk is increased, incorrect charging perameters or inadequate cables or lack of overcurrent protection ( fuses), or just poor engineering practice.
However all ready built lithium batteries have built in battery protection circuits, the BMS. This will limit the current and thus energy, that the battery can accept or deliver. Provided the BMS is functional the cells in the battery are protected from overcurrent, over voltage and over temperature. Regard the BMS as a last line of defence, add external overcurrent protection and only connect suitable chargers and loads.

Mike

 

[rv888]

Thanks Mike for the detailed explanation. That is what I felt I had read from everything, but felt maybe I was missing something. Those videos Ernie mentions are ones I had previously watched and while they are somewhat good they did add to my overall concern which lead me to ask these questions. Thanks again everyone!

 

[mikefitz]

From the video using 12v car adapters seems a tedious and perhaps slightly dangerous method. At 10 amps, car type 12v plug and 8mm connectors are operating at the top end of their power capability and as shown in the video the cable quality is suspect, no charging cable should get warm. The car type 12v plugs and sockets often overheat and fail due to poor contact area and low quality. In practice any current over a few amps through these type of plugs and sockets will result in unreliable connections and possible melting plastic

Its not clear what appliances you are powering during loss of utility power but low cost 12v power converters are available for USB outlets and laptop charging, these connect via fuses direct to the 12v battery.

If AC power is needed an inverter running from the 12v battery could be an option.

For charging the Yeti, using the Anderson input rated at up to 50 amps would be a safer and faster than using car chargers. Connecting a battery to battery charger between the 12v battery and the Anderson input would seem to be an effective technique. A 20 amp charger is not too expensive, (Renogy UK)

12V 20A DC to DC On-Board Battery Charger

12V 20Amp battery to battery chargers are designed for charging 12V batteries.The 12v battery charger charges AGM, Flooded, Gel,and Lithium batteries!

uk.renogy.com

Goal Zero units and chargers have been known to overheat whilst charging is taking place. This can happen with any type of battery and charging system so undertaking a risk assessment on possible danger is prudent, example, smoke detectors, suitable fire extinguishers and escape route.

Mike

 

[Warpspeed]

The batteries themselves seem to be inherently pretty safe, its how they are used that seems to cause all of the problems.
If you keep your batteries within a sensible temperature range (within the human tolerant temperature zone) and keep within the flat part of the voltage characteristic, you cannot go too far wrong. The risk of an uncontrolled high current discharge can be easily mitigated with a fuse.

If you can do all of that, your batteries should lead a long and happy life. Straying outside the (battery) comfort zone can lead to permanent irreversible damage. That can be either in very small increments spread out over time, leading to a gradual degradation, or a one time big accident such as gross over or under voltage, which will definitely result in sudden complete irretrievable battery death.