fiat 500e knowledge base

Lithium Battery bests practices

Lithium Battery bests practices by Peter Wolf.
How to prevent Li-Ion battery for loosing SOH and ageing? How to not visit HV Battery service.
Sorry for the mistakes, I will work on it

I have started my adventure with lithium batteries about 20 years ago, as a RC modeler. Lithium batteries that we used in flying models, unlike laptop batteries, were designed for maximum current, delivered in a very short time. Thanks to this I gained experience with the most well-fed Lithium batteries in the world. Batteries that I use for acrobatic or racing models are able to temporarily spend up to 100 times more current than the nominal capacity.
What does it mean? For example, use a small battery used in 250 class acrobatic drones with a capacity of 1300mAh on 14.8V what means 4 cells per 3.7V nominal.

Next to the capacity, a thick 75C inscription appears, marked with a black background. This means that, we can temporarily pull the current ,75 times larger than its capacity.
That is 75 * 1300mA = 97 500 mA.
Almost 98Amps on 15V what gives 1470W from a battery not much bigger than a matchbox.

RC LIPo Battery

100% SOC is actually 100% capacity of our battery and 0% is 0%

In your mobile phone for 99,99% it is. that’s why a mobile phone battery lasts only for two years. 100% for 4.2V(or even higher to 4.35V) and 0% for 3V.

In most EV vehicles, the original cell capacity is degreed for longer battery life. And for example Fiat 500e’s 100% SOC is equal to ~4110mV/cell and 0% is around ~ 3300mV/cell

Lithium battery haven’t ‘memory effect’. There is no sense to discharge them to 0% and then full charge.

Charge Voltage Limit and Discharge cycles

Charge Voltage Limit is also very important. Every reduction of 0.1V in max cell/voltage double the battery cycles. Every 0.07V (70mV) drops the usable capacity by ~10%

Charge level
Discharge cyclesStored Energy
4.25200 – 350105-110%
4.20300 – 500100%
4.15400 – 70090% to 95%
4.10600 – 100085% to 90%
4.05850 – 150080% to 85%
4.001200 – 200070% to 75%
3.902,400 – 400065%
3.804000 >55%

Deeper discharge, shorter life.

Deeper discharge (100% DoD equals to full cycle) = shorter battery life – less battery cycles. Operating the battery in mid-state-of-charge would have beast results.

(Depth of discharge)
Baterry cycles
Battery cycles
100% DoD~300~600
80% DoD~400~900
60% DoD~600~1500
40% DoD~1000~3000
20% DoD~2000~9000
10% DoD~6000~15000

Lithium battery charging and balancing

No Lithium battery archive ‘capacity memory effect’ therefore it is not necessary to always discharge to zero and charge to 100%. and it will definitely be better if we don’t charge like that. If you do not use 100% daily, consider setting a charging schedule so as not to recharge the battery every day to 100%. Try to keep the limits from 20 to 80% State-of-Charge. You don’t have to worry about the battery being unbalanced. Discharging to zero and charging to 100% has nothing to do with balancing the battery. Fiat 500e balances the HV package whenever it is needed, even during sleep cycle

Fiat 500e HV battery balance data.

Lithium batteries storage

Lithium batteries differ from each other, the additives used, which every manufacturer keeps secret… Lithum Polimer batteries, achieve their incredible performance at the expense of stability and explosive nature. These batteries, whose purpose is to discharge from 100% to zero in 3-4 minutes are extremely sensitive to too low charge or high charge. The only way to store these batteries, as well as all other Lithium batteries, is to charge them to the “magic” STORAGE level of 3.75V – 3.82V per cell (about 50%SOC)

Proper prepared to store Lithium batteries can be stored up to 5 years, almost without degrading the battery SOH (State-of-Health) Remember, or notice the next time, how much charge your new mobile phone has taken straight out of the box?

For any Lithium Battery bests practices, remember, no lithium batteries like to be 0% or 100% too long. And the closer to the center (SOC: 45-50%) the better. Depending on the additives used for the chemical composition and battery pack build. Lithium batteries can only be more or less resistant to too high or too low SOC.

Putting battery in to Storage State requires a special charging mode. it is mainly used for batteries used from time to time such as drones/RC batteris, which we charge to 4.2V / cell just before use.

to be continue….

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