Several Days No Sun, 0 F Temps...How Do FWC Batteries React?

[Wallowa]

Just returning from an extended trip in Hawk with AGMs and noted a lot of variance in available watts from batteries in cold temps.

What has been your experience with AGMs [lead/acid] and LiFePo4 batteries when temps of batteries are very low and no sun for solar or 110 hookups? Nor running alternator in truck to recharge.

Specifically how did voltage and SOC change with loads and over time? Rate they dropped, rate they rebounded to and to what level?

Thanks....

Phil

 

[ckent323]

The charge and float voltage in the cells making up the battery varies with temperature.

See

https://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures


"Freezing a lead acid battery leads to permanent damage. Always keep the batteries fully charged because in the discharged state the electrolyte becomes more water-like and freezes earlier than when fully charged.

According to BCI, a specific gravity of 1.15 has a freezing temperature of –15°C (5°F). This compares to –55°C (–67°F) for a specific gravity of 1.265 with a fully charged starter battery. Flooded lead acid batteries tend to crack the case and cause leakage if frozen; sealed lead acid packs lose potency and only deliver a few cycles before they fade and need replacement."


See also

https://prod-ng.sandia.gov/techlib-noauth/access-control.cgi/2004/043149.pdf

 

[Vic Harder]

That Sandia study, page 10 has a chart that nicely shows how the effective battery capacity decreases with lower ambient temps.

I'm not sure that accounts for Phil's observations though, from his previous thread on this topic. He was seeing vastly decreased battery voltage with minimal draw.

 

[Wallowa]

Ah, the 'mystery' of batteries and chemistry! At the end of the trip with only a mild 24 degree battery temps [lowest was 13 F..that I know of...] the batteries bounced back, from running the furnace, quickly to the nominal 12.8 volts from a low of 12.55V...SOC never went below 90 %...Craig no significant recharging possible for days... no sun and no driving...

How will my soon to be Li battery [June 4] react to the same set of temps, load and no recharging? Will the SOC drop while the voltage will stay higher?

All comes down to watts and if batteries fail to punch out amps, volts mean nothing...volts can only push out available amps...my best guess is that my AGMs are damaged and once damaged they stay damaged as I understand.

Faced with no incoming amps and a load during low temperatures are Li better than AGMs?

And more importantly is there anything to mediate possible battery damage to either type battery under low temp conditions?

Thanks...Phil

 

[Dessmo]

I recently replaced my Victron gel batteries with lithium a 100AH LifePo4 battery. So fare I find that the lithium battery are much better in almost all ways. I live fare north with close to no effect from the solar panel in Nov-Feb. Lithium is less effected by the cold, my batterie worked fine with an outside temperature down to around 0F. The BMS protects the battery fro getting damaged, and the BT gives a good overview of consumption, power left and the health of the battery. Don’t think you will get this information with an AMG battery even if you have a shunt and a battery monitor. The biggest challenge I see with lithium is charging under cold conditions. My battery can be charged down to 23F, when it is colder than that the internal heat system is activated. But my experience was that the effect from the solar panel was not enough to heat the battery and charge it. I have now insulated the battery so it better holds the heat and will charge during the day even if it is cold. If required, I start the truck and the power from the DC2DC will heat the battery until it can be charged. With my 100 Ah lithium I have 95Ah available, but with my 120Ah gel only 60Ah. And the lithium can take more than 3000 charge cycles, way more than any led acid battery.

 

[Wallowa]

Dessmo,

Thanks for that information...tip on heating battery to minimum temp that allows charging by starting vehicle and DC/DC charge heating battery is a valuable idea. I agree my Victron 712 and Zamp controller really don't reflect the health of my AGMs....well, they do when the batteries don't deliver the Watts nor recover....

Norway!...On our Honeymoon in '04 we spent 40 days in that beautiful country...train Oslo to Bergen and then renting a car and driving all over Western coast and Fjordland...loved the "Everyman's Right" and camped across your outstanding country....

Appreciate the input..

Phil

Ps...Was going to use Li batteries [less weight] for my off road motorcycles but cold sometimes prevents the bikes from starting as batteries are 'asleep'...trick used on bikes is to turn on headlight for a load that generates enough heat to coax watts from the battery to start the bike...I kept my AGMs on the bikes...