Li-ion - LiFePO4 - car battery

[Thuppu]

Any experience with these small and light 12V Li-Ion LiFePO4 batteries in car use? Seems that even an really small 5Ah battery is enough for starting an car engine, but probably so small wouldn't last for long..? Starting amps goes well over the specs... I have been looking for a battery in 20Ah size, it should have enough grunt to start the car for several times in a row. But what about the charging rate(C), can a LiFePO4 battery in this size handle the car alternator charging?

[M2ki]

Forget li-ion and lipo if you dont want burn down your car and/or garage.

Typical 20Ah LiFePO4 has max discharge 3C and max peak 10C for 5 seconds. 200A is joke for a car battery in the north.
Optimal charge is 0.5C and maximum charge is 1C with temperature monitoring.

[Thuppu]

LiFePO4 should be quite safe. Nothing near as dangerous as "RC" LiPo batteries. Was thinking more of using as a trackday battery and summer use.

For example this battery has been proven to work well: https://www.rennsportshop.com/de-top...A-LiFePo4.html

[M2ki]

Your link says that this battery should be charged only with a special charger.

If you want to charge it on a car you need somekind of special charger between the alternator and battery.

[Thuppu]

Special charger is just so it stops the charging when the battery is full. Other wise no difference from a normal charger. Car alternator voltage isn't a problem. And I guess the charging amps depends on how empty the battery is..? If the battery is empty then aalternator will charge with high amps and when battery is close to full(close to max voltage) it will drop amps down..? Have I understand right?

Some batteries has charge rate 3C or more. 3C 20ah would be 60A. Also ssome batteries has smart electronic and protection.

[Thuppu]

The 8ah battery in the link is 10C so it makes 80A charge rate.

[M2ki]

Some batteries has charge rate 3C or more. 3C 20ah would be 60A. Also ssome batteries has smart electronic and protection.

These batteries have no electronics and no protection. You have to somehow switch claimed 550A if you want protection.

If your charge voltage will be around 14V and the battery can take 10C charge as claimed, it should work.

[Thuppu]

Quite strange there is no more interest in these? 20-30kg vs 1-3kg and much smaller size. Seems there is quite good experience in car use even with the small 5Ah sizes...