Lifepo4 and temperatures below zero

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southwick asked Jul 21, '19

Lifepo4 and temperatures below zero

I intend to install in my campervan the following setup:

Victron 100 Ah Lifepo4 battery
VE.Bus BMS
IP22 main charger
75/15 MPPT solar charge controller, along with two 100W solar panels.

I do, however, still have a number of question to which I so far get only vague and contradictory answers. The questions are about what to do in a situation in which our campervan stands on a indoor parking lot with temperatures that may be lower than zero degrees.

It is clear that the battery should not be charged below zero (better five) degrees. But then:

Is it OK if an already fully charged battery keeps connected to the main charger by temperatures below zero degrees?
Does keeping the battery connected to the main charger for longer periods have impact on the life time of a Lifepo4 battery and, if so, how big is this effect?

Disconnecting and removing the battery is not a realistic option. The battery is hard to reach and it is only about a max of 4 or 5 weeks that we do not use our campervan.

Thanks in advance for helping me out!

Lithium Battery temperature

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Answer 1 · 2019-07-21T11:52:12Z

southwick answered · Jul 21, 2019 at 11:52 AM

See question above

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klim8skeptic ♦ commented · Jul 21, 2019 at 12:27 PM

#1. Don't charge Li batteries near zero, even maintenance charging.

#2. The longer Li batteries are held at 100% SOC/upper voltage limits reduces battery life.

"Disconnecting and removing the battery is not a realistic option. The battery is hard to reach and it is only about a max of 4 or 5 weeks that we do not use our campervan."

Ideally Li batteries placed into (long term) storage should be at 50% SOC.

Small normal discharge/parasitic loads (BMV/BMS/cell balancers/etc.) can drain your batteries to dangerous levels in a few months.

Is it worth the risk to your batteries from improper charging/maintenance?

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Answer 2 · 2019-07-21T12:18:15Z

kai answered · Jul 21, 2019 at 12:18 PM

Connecting an active charger to a battery when temperature is known to be out of spec seems to me to be a marginal design. I'm unaware of any publicly available data on quantifying the impact, someone else may chip in.

Have you considered:

1) Insulation + heating system that keeps the battery above 5C, and/or

2) Installing a disconnect on the battery's wiring beyond its fuse. This way you can isolate the battery without getting to the battery when its unattended, or

3) Automatically disconnecting/disabling the charging sources when temperature is below a trigger point.

Are you likely to be using the campervan when the temperature is below 5C, or is that when its in the parking lot (and unattended)?

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Answer 3 · 2019-07-25T05:43:41Z

southwick answered · Jul 25, 2019 at 05:43 AM

Thanks for the responses!

I guess that a switch to disconnect the battery is the easiest way to deal with the storage issue. If the campervan is out of use for a longer period I could check the battery every now and then, and disconnect the battery when the SOC has gone down to a level of say 60%. The remaining loads are that small that they might not cause a problem within a period of a couple of weeks. This is, however, not an ideal situation.

What also remains is the temperature problem. If I want to use my campervan again after being out of in winter, I might have to heat the battery before I am even allowed start the engine. This is not the kind of flexibility that one associates with having a campervan!

Despite the undeniable advantages of a Lifepo4-battery, this makes me thinking that I maybe better stick to my gel battery as long as no solution has been found for both issues.

Somewhere else in this forum Boekel suggested that the charger should have a possibility to keep the SOC on about 50%. In combination with a function to keep the battery at a certain minimum temperature if it is connected to a charger, this would entirely solve the problem.

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