992 Turbo S flat lithium battery. What to do if this happens to you...

[jeffpeck]

Malarcy - my sequence for using footwell 12v socket for Ctek was/is; starting with ignition off, turn ignition on, then turn charger on, wait 1 minute, then turn off ignition & lock car. Ctek's first 3 lights come on and but go no further before error light flashes. This sequence worked OK for 992.1 4GTS but won't with 992.2 4GTS.

 

[GM_991_2_GTS]

Hold the button on the Ctek. It'll change the operation from 'charging' to a constant 12v supply. I haven't used mine in that way, but I'm going to assume after a few minutes you should be able to press the button again and return it to it's normal charging mode. If not, just switch it off at the wall and back on again.

Thanks for the information.

 

[GM_991_2_GTS]

I've picked up my 991.2 and confirmed it's a LiFePO4 battery. I also managed to pickup a CTek XS charger and have connected up the "CTek quick connector/charger" cable using the battery + and earth point on the battery clamp bolt.

On my 997 there was a place in the scuttle panel, where you could run, and hide, the quick connector so that you could access it from outside of a locked car. I am researching something like this on the 991 as it would appear with a flat LiFePO battery you need to overcome two issues, 1. opening the frunk using the fuse board method and 2. perform "defibrillation" to reset a completely flattened LiFePO.

This is from ChatGPT regarding charging LiFePO batteried.

Key facts about the CTEK Lithium XS and LiFePO₄ batteries​

1. It’s not a “trickle charger” in the old lead-acid sense.
   The Lithium XS is a smart charger. Instead of continuously feeding current (which would damage a LiFePO₄ battery), it uses an 8-stage program: charging, balancing, testing, and then maintaining with very low current pulses only when needed.
2. Safe to leave connected long term.
   CTEK explicitly states that the Lithium XS is designed as a “connect and forget” charger/maintainer for 12 V LiFePO₄ batteries. Once the battery is full, the charger switches to monitoring mode. It will only reapply charge if the voltage drops below a set threshold.
3. Built-in protection for lithium chemistry.
   • No overcharging risk — it stops at ~14.4 V (safe for LiFePO₄).
   • Reverse polarity and spark-proof protection.
   • Can wake up a battery that’s been shut down by its BMS due to under-voltage.
4. Why this matters for cars
   Modern cars (especially with start/stop and electronics) need a stable, healthy battery. Leaving the Lithium XS connected while the car is parked ensures the LiFePO₄ battery stays topped up without stress or risk of sulfation (which only applies to lead-acid).

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Bottom line​

Yes — it is completely safe (and recommended) to leave your CTEK Lithium XS permanently connected to your car’s LiFePO₄ battery. It doesn’t “trickle charge” in the old sense; it intelligently monitors and only charges when necessary, making it ideal for long-term maintenance.