2008 XK , replaced whiney alternator and 8 year old battery. All seems much better.

It is driven weekly as a second car but can go a week sitting. Live
in a condo and have a builtin c-tek.
HOA frowns if i leave it constantly charged..

Have gone 5 days with no issues.. can I expect a week? Longer? Before it running down?

 

I don't have a place to connect my C-tek. I'm sure you've heard the routine. Shut off stereo. Shut off AC. Shut off the screen (no logo). Lock doors. Have a 2 yr old battery which charges to 13.1. Driving charges to 12.8 ish. I get a week before voltage drops below 12.5. Car still starts for a second week but battery near 12.3

 

Worth checking the quiescent current (after about 30 or 45 mins). So long as it is tiny the battery will last quite well, otherwise fix the power drain (or use ctek etc).

 

Mine'll go two weeks without help, but then a good long drive is needed to get it back up a bit. If I can't drive for a bit, I throw it on a CTEK for about a day and all seems okay for another week or two.
If I DON'T drive or CTEK it for over a month or two, I'll bust out my actual CHARGER and let it charge until 10 amps says it'd complete. Sometimes that takes a day. Schumacher 2-10-40-200 unit.

 

Since I purchased my car 11 years ago it has constantly been on a CTEK. My first battery was so old (original Jaguar battery) I changed it even though all was well. I now drive almost daily. If you don't drive the car and you listen to the above instructions.....Always lock the car as soon as you get out of it......Drive a fair distance once a week or so.....If the battery is fairly fresh (under 1.5 years or less) it should last close to 2 weeks before going dead. Problem is.....you don't want it to go dead, because that might be the condition of the battery once you want to get it started again and running as it was...DEAD. I feel for you, if your community frowns on a charger...What about electric cars???? Our cars do have a parasitic drain which is normal for our cars but probably high for other cars. If you have an electrical issue...than you have another issue. You should be good for 2 weeks especially on a 2008 which I believe had a smaller drain than the 2010+... Good luck and let us know how you make out. PS....If you have an Indy doing work for you, try to ask politely for him to keep the doors closed and locked when not being worked on.

 

Is it hard on the electronics to start w low battery voltage? The car starts immediately w/ 12.2 then the alternator kicks in 14.5 I wish I could keep the car on C-tek (13.2) but don't have the option.

 

Mine goes 3 mo. no issues.

Do the math, 850CCA battery, and quiescent drain in the order of mA.
Cheers!

 

Here is the technical, but not real life experience answer:

Starting a car with a low battery voltage can indeed be hard on the vehicle's electronics, though the extent of the impact depends on several factors.
Here's a concise explanation...

Strain on Electrical Components: A low battery voltage (typically below 12.4 volts for a standard 12V car battery) forces the starter motor and other electrical systems to work harder to compensate for the reduced power. This can cause increased current draw, generating heat and stressing components like the starter, alternator, and wiring.

Voltage Drops and Spikes: When starting a car with a weak battery, the voltage can drop significantly (sometimes below 10 volts), which may cause sensitive electronics, such as the engine control unit (ECU) or infotainment systems, to malfunction or reset. In rare cases, severe voltage drops or subsequent spikes (when the alternator kicks in) can damage circuits or modules not designed to handle such fluctuations.

Battery Damage: Repeated attempts to start a car with a low battery can further degrade the battery itself, reducing its lifespan due to excessive discharge cycles.

Modern Vehicles: Newer cars with complex electronics (e.g., sensors, ECUs, and infotainment systems) are more sensitive to low voltage. Most modern vehicles have voltage regulators and protective circuits to mitigate damage, but consistently starting with a weak battery can still cause long-term wear or unexpected failures.

Mitigation: If the battery is low, using a battery charger (I know you can't) or jump-starting properly (following manufacturer guidelines) can reduce strain. Avoid repeated start attempts without giving the battery time to recover or recharge.

In summary, while occasional starts with a low battery may not cause immediate damage, it does stress the electrical system and can lead to premature wear or failure of components over time. Regular battery maintenance and ensuring proper charge levels are key to protecting the car's electronics.

 

3 months ..awsome..

one week is probably the longest i have to go...

It drained 3 times since I bought it with an 8 year old battery..

It's my 3rd XK..but the other 2 were couple years old not 17!

 

Luckly, my 2008 XKR can go 3 weeks, then needs a drive to go another 3 weeks. But the car must be locked down, ears tucked! There are rare times I get gremlins, so I take a short drive, restart, and all good. Battery is at least 4 years old, time to replace it.
Rick

 

When my cold battery reads 12.4v... it is replaced.

 

how many years on the average is that??

Obviously my 8 year old battery was too long..

Started with various components like cruise and infotainment nit working properly..

That was my hint to replace it..which i ignored due to ignorance on older XKs.

 

8yrs is good for these cars, which are not kind to batteries.

 

Problem being it might start but then you'll have a LOOOOOOT of troubles and electric gizmos...
And trust me it can go far..Such as the car suddenly going in safe mode, limiting the speed to 20km/h even though you're on a highway or a roundabout! (it happened to me). It will see troubles with the EGR, the brakes, the TPMS and all...even though all is fine..
Trust me, it's scary ...I've had the battery changed and it's now fine but the car is always stressing me now...

 

To save your sanity, you should give your car to me.

 

[QUOTE=Tiepolo;2861045]Problem being it might start but then you'll have a LOOOOOOT of troubles and electric gizmos...
And trust me it can go far..Such as the car suddenly going in safe mode, limiting the speed to 20km/h even though you're on a highway or a roundabout! (it happened to me). It will see troubles with the EGR, the brakes, the TPMS and all...even though all is fine..
Trust me, it's scary ...I've had the battery changed and it's now fine but the car is always stressing me now...[/QUOT

Know that feeling....the constant "what's going to happen next"..

Confident my solutions will work..

3 weeks no issues....

Feeling better...

 

OE battery. 4 - 5 years.

 

Here is a rough estimate, given your new battery and alternator:

(Length of time sitting, Cumulative Battery Drain, Battery Resting Voltage)

1 day ~1.2 Ah ~12.6V

5 days ~6 Ah ~12.3V

7 days ~8.4 AH. ~12.2V

10 days ~12 Ah. ~12.0V

14+ days. ~17 Ah. Risk of not starting
~df

 

Thank you!!

Looks like barring any issues i should never have
a problem since it is driven twice weekly all year long...

Keeping fingers crossed 🤞

 

and how did you calculate this?