Our lovely Polestar 2 started showing mystical electrical symptoms recently with no clear common cause. The first were faults in the rear lights and the turn indicator light system. The car complained about the problem with a visual warning signal and a sound indicator every time when using the turn signal, which was quite tiresome and frustrating. I took the car early to yearly maintenance to the shop (Bilia) to take a look at the issue, but the issue was not ongoing then, and the technician said that they could not trace the issue while it was not active. But, the technician instructed me to visit the shop during office hours if the issue resurfaced.
Fair enough. After the maintenance visit, the issue came back after a day or two, and I took it for a quick check to the shop [0], Even though the fault was active, the technician could not find the cause, and we agreed on a new time with a specialist electrician with an extended slot for diagnostics. I was warned that the diagnostics alone could cost several hundred euros.
| [0] | This is actually very good service, as is the OmaMekaanikko system Bilia has in place. Basically you have the same person maintaining your car every time you visit, so they should gain familiarity and know the ins and outs of the vehicle... as much is possible when seeing the device once every three years or so :) |
After the visit, I noticed two new issues; I could not remotely start the air conditioning to heat up the car and the car did not charge if scheduled for a night charging. Everything worked otherwise and the airco and charging worked when started without the remote or scheduled operation.
I discussed the problem with some friends and similar strange symptoms in car electrical systems had been caused by a dying 12V battery.
I investigated a bit how to access the 12V battery and how to measure it. I decided to measure the 12V battery voltage to see if it was bad.
I measured the battery using the charging points for the 12V battery. It reported 12.5V, which should be fine. But, I knew from reading other reports and how batteries work, that the simple voltage difference doesn't tell the full story, and under load the battery might still be dead. Because the expected cost for the diagnostics in the shop was so great, I was willing to replace the battery; it would not make matters worse and would eliminate a line of investigation, even if the replacement did not solve the issues.
I found a bit of prior art about changing the 12V battery, which gave me confidence to do this myself. I could not find any warnings about messing up the computer systems or having to deal with some pairing issues between the battery and the car, so I felt the risk was minimal.
Battery specs from Polestar online manuals
| 12 V battery specifications | |
|---|---|
| Battery type | H6 AGM |
| Voltage (V) | 12 |
| CCA (A) | 760 |
| Size, L×B×H | 277.70×174.40×188.50 mm (10.9×6.9×7.4 in) |
| Capacity (Ah) | 70 |
I should have checked also this post before diving in to access the battery, now I did it without foreknowledge about what to expect.
The other M10 bolt in the bottom of the frunk was stuck badly and I could not open it immediately with the tools at hand. I managed to bend the bolt a couple of millimeters before giving up with the hand tools and deciding to visit the local tool shop. I bought a new 10mm socket with 1/2" drive to allow it to be used with my Bosch cordless impact wrench. The wrench has a torque suited to open bolts for truck tires, so I was sure it would open the bolt, I was just not sure if it would break something else in the process. With the socket, the bolt opened easily, luckily without any collateral damage.
Removing the battery was easy. First I detached the negative pole, then the positive. This is the order you want to do it [1]! There were two bolts on the sides of the battery and two in front keeping it in place. After unscrewing the bolts, I removed the old battery and put in a brand new Exide [2] with the same specs as the original Polestar battery. Installation was done in reverse order. I was warned that I could need to "pair" or "introduce" the new battery, but thankfully Polestar is not a BMW :)
| [1] | The negative pole is basically the zero or "ground", and the chassis of the car is directly attached to it. If you open the positive pole first, any metal object touching the positive pole while the negative pole is still attached, will shortcircuit if any part of the chassis is touched. You DO NOT WANT THAT. |
| [2] | Exide Dual AGM EP600 70 Ah / 760 A https://www.motonet.fi/tuote/exide-dual-agm-ep600-70-ah-760-a-akku-p278-x-l175-x-k190?product=90-01505 |
Immediately after the change, the air condition remote control worked, turn signals were not complaining and also the battery timed charging worked. There were still some residual issues with the rear lights, including a short fault indication the next day in the highway, but that lasted only for couple of seconds. During a drive later in the day, there were no issues.
I hope the weird problems went away with the battery change. I guess we'll see after a couple of weeks if the symptoms resurface.
Thanks to @hamatti for inspiring me to blog after a long pause.