I absolutely love the BMW i8. The fact that it’s a hybrid and looks as cool as it does makes it almost the perfect pairing. In my previous blog, I mentioned that one of the first things I wanted to check was the condition of the 12V battery – Supercar Ownership: The Unexpected Fixes & Mods I Didn’t See Coming.
I had read online that if your 12V battery is old and not holding charge well, it may start drawing power from the EV battery and, in turn, pull down its range. However, I couldn’t find too much concrete information on this. Some sources suggest that this only affects newer models in the series. But just in case, I thought it would be good practice to check and change the battery.
Why Change the Battery?
It’s often recommended to replace the 12V battery every 3-5 years, and considering my i8 is almost a decade old, it was well worth investigating. When buying an older car, it’s always wise to ensure that key maintenance items like this have been addressed.
Going through the car’s paperwork, I couldn’t find any evidence that the 12V battery had ever been replaced. That meant it was best to get it checked and, if necessary, replaced before it caused any potential issues.
Getting It Done at SWSS
I took my BMW i8 to SWSS, a well-known Mini and BMW specialist in Cardiff. Having had many upgrades and MOTs for my Mini done there, I trusted them to handle my i8 too.
When speaking with the team, they informed me that the battery registrations were low. Essentially, every time a battery is fitted (or reconnected), the car logs this data. Without getting too technical, the data suggested that the battery was likely the original one from the factory—so it was time to get it swapped.
The cost of a new 12V battery, fully fitted, came to around £225. A small price to pay for peace of mind.
Any Immediate Differences?
Was the old battery causing any issues? No, not really. But I didn’t want to take the risk of it failing at the worst possible time—like being stranded on a country lane somewhere.
One of the big questions I had was whether replacing the 12V battery would affect the car’s electric range.
Did It Improve the EV Range?
This is where things get a little tricky. The first night I charged the car after the battery swap, I woke up to see one of the highest electric ranges since I bought it back in December. It showed 14 miles—not a huge number, I know, but for a 10-year-old early hybrid supercar, I was happy with that.
With temperatures remaining consistently low over the last few weeks, weather variations shouldn’t have played a part in this change.
However, the trip computer had also been fully reset, as had the car’s learning of my driving style. This means that it could simply be showing the maximum possible range, just as it did when I first bought the car.
So, did changing the 12V battery extend the i8’s EV range? There’s no definitive answer.
Final Thoughts
What I do know is that it was time for the 12V battery to be replaced, and I now have peace of mind knowing that it won’t unexpectedly fail on me.
The inspection report from SWSS did highlight a few other issues with the car—but you’ll have to wait to find out about those in a future blog.
For now, I’m driving the i8 with confidence, at least from a battery perspective!
