There’s a lot of misinformation out there, especially when it comes to the X351 series which are a large car with often large engines and complicated electrical systems.

The first bad advice out there is using the under the hood fusebox “+” terminal to jumpstart your car. That’s only for the purpose of opening the trunk if your battery’s completely dead.

The second is don’t call roadside service unless they’re willing to use jumper cables from their truck engine. A dead battery isn’t going to get much out of these little portable battery packs that all tow-truck drivers seem to use now! They are typically 6000 maH (Milli Amp Hours—a milliamp being 1/1000th of 1 amp. Sounds much more impressive though; right?) I had a tow truck driver try to tell me it was ‘6000 amps’ which would’ve killed him if he touched it!)

I’ll be honest, I don’t know the engineering/science behind taking such a low amperage and converting it to hundreds of cranking amps—but then again, I’m kind of ignorant on how ballasts manage to increase a small amount of voltage to something several times higher, such as for for Jaguar’s HID headlamps, (From 12v) or even fluorescent lamps. (From 110v)

But using two roadside services for two attempts from two different tow truck drivers using crappy little battery packs wouldn’t start the car. Of course both of them immediately said ‘It’s the starter’. (And mind you even an Uber Driver can become a tow truck driver nowadays. So it’s not like they’re all mechanics driving around to fix our cars. Many, many decades ago, yes!) Since I couldn’t get anyone to give me an actual jump using cables and a decent size engine. I just replace the battery because it was probably close to its end of life anyway once I did that, and then reset the brake using a scan tool programmed for jaguar; it started right up!

So don’t believe everything someone tells you because there were no codes that anything was wrong with the car. And if I would’ve followed her advice, I would’ve spent several hundred dollars just for the privilege of paying for a new battery anyway. (And it’s possible if I could’ve got a decent jumpstart I wouldn’t of had to buy a new battery. But I probably would’ve had to soon enough.)

 

mc690, if you have electrical questions, please let me know. I will do my best to give you an answer that you can understand. As for how these "little" battery chargers can crank out 100's of amps to start a car is something that can be misleading if you don't have the write values. I think what you really had was a 6000 mA-H battery. Not a 6000mA battery. A 6000 mA-H battery can provide say a 100 mA load for 60 hours (100 x 60 = 6000). But, if the battery is capable, it can provide 100 amps for 0.06 hours (or for 3.6 minutes). The battery just needs to be able to discharge its stored energy really quickly. Not all batteries are capable of doing that. But, you build it right, it can. Now, there are certain limitations and how the battery is constructed will determine how well it does at higher power. NOt to mention, when you start pulling these high currents, the actual power you get out of the battery drops So, that 6000mA-H battery may only actually output the 100 amps for say 1 minute, not 3.6 minutes like my initial calculation states. If I need to explain things differently because you are not getting what I am saying. just say so. I can come up with a few different ways to explain this concept.

If you want to know how the ballast works for an HID bulb, I can explain that to you too. Just let me know what you want to learn.

 

You’re right; I remember seeing maH & wondered why it was different when I voice transcribed my post. But the premise is still correct. Our version of the British Tank still needs more power than those are capable of. But road services use them because they are fine for most vehicles.

But I also know older Jaguar’s can play the stereos for several hours. I’ve owned two X351 series (Out of Seven.) & neither could stay on for even half an hour! So I stand by what even Jaguar recommends in the Handbook, jump starting from another vehicle (And probably the one Mr. Bean drives!) Cheers & Merry Christmas and a Happy New Year!

PS: And I know the driver was full of himself claiming it was six thousand amps!!!! Any tow truck drivers want to prove me wrong go ahead & grab onto six thousand amps. I’m wondering if that will be self-cremating?!? Let me know!