Today I collected a family member's 2001 S-Type Sport 3.0 in a 48-hour carpark where it has been sitting for a day or two before we went into Level 4 Lockdown five days ago. The battery was flat - door lights went on, but cranking was a click. The battery has a number code 1811 which may mean it i was made in Nov 2018, and it is a DIN65ZLMF 63 Ah whereas looking up the specs online seem to call for a DIN88ZLMF 80 Ah. It took about 8 hours to bring up to 100% and tomorrow I will hook an Autel 808 on it to see voltage.

My question is: I own a 2004 x350 XJ6 that is very sensitive to battery voltage, and my indy recommended it be changed when its voltage dropped to 12.1. Is the S-Type similar in its sensitivity to voltage? Are there electric bits that slowly drain a battery and if the battery is weakening, would they drain it to "click start" after about 5-7 days? In other words, is it likely to be the battery, or is there something stuck on that might be abnormally draining the battery?

 

Two peas in a pod in terms of sensitivity to battery voltage. I have seen three year old batteries go bad. The car may well need a new battery, if your scenario repeats itself.

 

You could test the (quiescent aka parasitic) current after 45mins - read the threads about how etc.

12.1V is very low, almost dead, but what matters is how low does it sag on cranking.

 

The 2003+ models are quite sensitive to low prestart voltage, and will commonly generate fault messages for the Electronic Parking Brake, Cruise Control, and Dynamic Stability Control. You can kinda think of those messages as the canary in the coal mine, providing a heads up that battery voltage is on the low side, long before the starter misbehaves. The early models? It's a different story, and are much less likely to offer any early warning until the battery gets so low that the starter will not respond properly, as you have experienced.

Determining battery health and state-of-charge by a voltage reading? That is only a VERY rough guide, and can easily give you misleading results. You can mistakenly think a good battery is bad, and visa versa. It's better than nothing, but before changing any parts, I'd troubleshoot a little more thoroughly.

At the very minimum, charge that poor battery before any troubleshooting. I'd then suggest having it tested. Most auto parts stores will do so for free. There are two main types of testers, resistive and capacitive. Each has its strengths and weaknesses, but generally the capacitive style is more accurate. It's also better at catching a problem before the battery totally fails, so make sure that is the style they use. If you ask and the guy scratches his head in response, he has no business testing batteries. Thank him for his time and try elsewhere.

If the battery tests good, there are a few other factors to consider. The charging system may be marginal, and is not letting the battery reach a full charge. This is easy to check. With the engine at idle, lights and AC on, you should see about 13.5V at the battery. If less than that (and the battery was already fully charged as previously suggested), your charging system needs some love.

If the battery and charging system both check good, consider your driving habits. Short, infrequent trips with high electrical loads (lights, HVAC, etc.) may not give the charging system enough time to fully recharge the battery after engine start. If that's the typical driving pattern, there may not really be anything wrong with the car. You may want to consider a battery tender in that case. Here's one option:

https://www.jaguarforums.com/forum/s...ng-port-87362/


The next thing to consider is a fault draining the battery while parked. After about 45 minutes or so, the various computer modules are supposed to enter sleep mode and draw only very minimal power. Occasionally, a module may not behave and stay awake. Or you may have an accessory inadvertently drawing power when it shouldn't, such as an aftermarket stereo. Details here of how to check for battery drain, see the PDF attachment in the first post:

https://www.jaguarforums.com/forum/s...-drain-123535/


Do consider by letting the car sit for a while, you've changed the pattern of usage. If the car is driven every day on trips maybe 20+ minutes, the charging system may have been able to mask a tired battery or medium level overnight drain. But let the car sit unattended and now the problem becomes apparent. I remember several years ago when a family friend went into a panic with her car. She drove it every day on a fairly lengthy commute, and it always worked well. But then she left it for several days while on a trip and the battery was dead upon return. She couldn't understand why, as it always started reliably when driven daily. I tested the battery for her, it had changed from useful component to awkward paperweight. The change is driving pattern is what forced the problem to appear. Normal troubleshooting quickly identified the problem.

 

Charged 8 hours. Let sit 12 hours. 11.7v. Started car 13.9V - charging system OK. Turn off, drops down to 12.3 in 20 minutes. Cleared a bunch of historic OBD error codes that look like a weak battery triggered them.

Looks like its time for a new battery as soon as Lockdown ends.

Thanks for the information.

 

Careful there before condemning the battery. Was the battery installed when you measured 11.7v? Or was it disconnected? If still connected, you could have an external drain that is slowly discharging a perfectly good battery.

Same with the 12.3v reading. If still installed, that relatively minor drop could be from the normal drain of the various computer models not having entered sleep mode yet, which normally takes 30-45 minutes. Once this normal drain stops, a good battery will self-recover somewhat, hopefully to the 12.6ish you’d want to see.

 

All Jags are sensitive to battery problems of low voltage. Batteries are too cheap to play around with a bad one.

TBB Dallas/ Plano