650s battery - car says needs charging, charger says full

[jerrytlr]

Hi all

Just wondering if anyone has come across this situation.

I foolishly let the battery get low on my 650s. It unlocks fine and tells me I need to charge the battery. It won't even attempt to start.

I have tried charging it with the McLaren (CTek) charger, which after about 1 hour told me the battery was full.

But the car still says the battery needs charging and won't start.

It has the upgraded battery and BMS, but the charger is the original one that came with the car.

Before I pull the frunk apart again, has anyone seen this before and if so, is there a simple remedy?

I have tried leaving the car locked for 24 hours, no difference.

[HIS LM]

Almost certainly the charger is duff had the same problem with my 650, invest in a decent c-tek and problem solved.

[ssray]

How old is the battery? If it's gone below a certain voltage it's knackered.
This is speaking from a two wheel point of view, bike batteries are made tiny with everything inside squashed together, it doesn't take much to warp a plate

[12pack]

As suggested, try another charger. In my case, it was a Ctek Li-ion one that failed while we were away. Putting on a brand new McLaren-badged one resolved the issue, but it took almost 10 days on charge to do.

[samoht]

With my 570 after the battery got low, the car would only start with the charger plugged in (ie while 'on charge'). Worth a try, although if your charger has given up then it may not make any difference.

[jerrytlr]

HIS LM said:

Almost certainly the charger is duff had the same problem with my 650, invest in a decent c-tek and problem solved.

I've ordered a new CTek charger - will let you all know if it makes any difference!

[650S]

I had this issue, on a 12c.

The BMS is messed up, and seems to prevent charging.

What I did was; pull the frunk liner, remove the negative terminal, attach the C-Tek to the + and - terminals directly.

After 4 hours it had 2 or 3 green LEDs,

Reconnected, started on the button.

175500 days overdue service

Date 1/1/1970

All corrected at next service

[Zingari]

The McLaren branded C-Tek chargers are rubbish in terms of long life despite the high cost for a 'premium' charger. There's no obvious signs they don;t work as hey will go through the process of analysing battery state, showing on 3/4 for several hours and then finish off 1/1 giving the impression they've charged the battery, when in fact they haven't done anything. I tried two, exactly the same. Despite my reservations (I believe C-Tek as a brand are overpriced and no better than a cheaper Chinese variants) I managed to pick up a new C-Tek Lithium XS charger cheap and decided to give it a final punt. It worked correctly straight out of the box.

By contrast I've got a Halfords trickle charger that must be 20yrs old and still going strong. Sadly it doesn't work with lithium.

[tobytwo]

Your Halfords charger will work with lithium if it can output around 14.2v, the BMS, which is inside the battery, will stop the charge when the battery is full. Older chargers struggle because lithium will make them work at max output continuously and they overheat.

[AA121]

These are recommended by V Engineering as a replacement for the original McLaren chargers which eventually fail.
https://no.co/genius5
They're available from most online stores but you need to remember to also order the cigarette lighter attachment separately. Also, make sure any make/model of charger you use (including CTek) is compatible with the lithium ion battery.