Not quite. It will perform the same as a higher capacity lead/acid battery (100 Ah in my example) in terms of cranking the engine over continuously. It will certainly be smaller and lighter - no doubt about that.
It's not ideal - a lead/acid battery of even the same capacity would last much longer with a continuous low current draw (e.g. parasitic drain from the on-board systems when parked). This may or may not be an issue in practice depending on the state of charge when parked, how often the car is used, whether it's kept on a maintenance charger, etc. But per the MBWorld thread that
@grober linked to an AMG GT owner in Germany felt it could do with more capacity:
Plus other comments about the setup:
You mentioned getting a quote for a new Li battery for yours when it was under 3 years old, but it wasn't 100% clear whether it actually had to be replaced then? Do you use a trickle charger?
The battery was draining very quickly and it took lots of head scratching because it would drain at home within 24 hours, but wouldn’t drain in 24 days at the main dealer. AMG technicians at the main dealer and in Germany were stumped.
It was eventually me who worked it out, there’s an option to connect your phone to the car for real time recording of telemetry data whilst on track. It turns out that my phone would be in WiFi range when ant home and maintain a connection.
The car wouldn’t go to sleep whilst the WiFi was active and so the battery would be isolated by the BMS. Hence when I’m the car was at the dealership my phone wasn’t in range and the car shut down as normal.
AMG Technical (Germany) asked that I leave it off the trickle charge until at least the problem returned, because they had wrongly assumed that the trickle charger was keeping the car awake, as that can happen if not wired in correctly.
They said the nature of a lithium battery meant that it could be left all winter without a trickle charger and it would start first time because the rate of natural depletion (without a drain fault) is almost zero, and would remain so for the life of the car.
They explained that the lithium battery is intended to last the life of the car, and replacement would only be expected to be caused by unlikely failure of the BMS not the battery itself, and hence the quote for a replacement battery (potential BMS fault).
I can leave it for 3 months (not on trickle) and it will fire immediately. I have similar cars with similar engines with AGM batteries and they moan if left for a month without trickle, I wouldn’t risk leaving them longer than 6 weeks with being hooked up.
AMGs advice was to alternate trickle charging every other week or two on the cars with AGM batteries, but to do it pop the lithium battery on charge no more than once or twice per year until it’s fully charged.
Almost all of the cars have a trickle charger but I follow the advice from AMG and periodically trickle the cars with AGM, and then disconnect for a while, as they said the exercise does them good. Cars with lithium stay off trickle.
One exception it all, is Ferrari Technical advice was to ensure that all cars regardless of battery type should be on a trickle when parked at home, even overnight. Still doesn’t mean they’ll start though because even on trickle they can discharge…
