moonstone
Tyre Kicker
After spending a few stints on the net over the last couple of days looking for definitive answers, I thought I'd share this so that others in the same boat might find this post on the net and it helps them.
My car was in at a detailers for a week and after getting a call to say that my BMW display key was showing as being flat and that he was charging it (makes no difference to opening and starting the car, but he didn't know that), he asked if I could bring the spare when collecting it that morning. The message on the key was a red herring, he'd run the car battery flat, so we stuck it on charge at the points under the bonnet and I arranged to collect the next day as I didn't need the car anyway. This is when I made a few discoveries about LI batteries in cars and so when I went back to collect I wasn't hopeful that the battery would be charged. I was right.
Lithium Ion Batteries - Self Protection Relay
The battery has a voltage management system. In order to protect the battery cells, when the voltage on the battery drops to between 10 & 8 volts, an internal relay triggers that disconnects the battery cells, so that whatever is draining the battery is stopped from doing so. This means that even if you apply a charger to the points under the bonnet specified by BMW, it won't reach the battery or the electrical system on the car, as the connection is broken. I have read that if you're able to apply a positive charger connection and then a negative to what's called "true ground" this may work to jump-start the car but I didn't try it.
The only way to reset the self-protection relay is to apply 12 volts across the battery terminal on the battery itself.
But my alarm's going off, so it must have power?
No. The alarm system has it's own, separate battery, so if you think there's must be power going to the car because the alarm siren keeps sounding after you've opened the door with the key, think again!
How to charge the battery?
You need to get access to the battery itself, which on most modern BMWs is located in the boot. You have two options here. 1 is to apply a 12volt power supply to the battery to reset the self protection relay and then try the jump start terminals under the bonnet. Or use a proper lithium ion battery charger on the battery itself. This is what I did and after about 5 minutes, the electrical systems came back to life and I was able to start the car. I've now got it sitting charging up on my drive just to restore the battery,
Accessing the battery in the boot?
On the M5 the only way was to use the key blade to open one of the front doors and the crawl into the back. The rear doors won't unlock from the inside due to the deadlock system. I then pulled down the centre armrest, to get half way into the boot, where I was able to access the pull switches to fold the rear seat's down. That then gave me access to the battery under the boot floor. if you don't have folding rear seats or ski access in the centre, then you're out of the luck and you'll need to talk to a professional for advice on how to get to the battery. On the M5 there's no emergency trunk release as found on the M4 either.
Swapping out a Lithium Ion battery for an AGM one
If you're in a the position that your battery is knackered and needs to be replaced, it is possible to swap it our for an AGM battery. This will not disrupt or harm the electrical systems in the car contrary to what you may read online. As with any battery change there is a specific BMW Workshop application (ISTA) procedure for a battery swap and for changing from AGM to Lithium Ion and vice versa. This must be carried out due to the differences in how the two battery types are charged and maintained.
The only drawback from swapping from an LI battery to an AGM one is that the AGM won't last as long and is much heavier than the LI equivalent. But where as an LI battery from BMW will cost in the region of £1000+ depending on where you get it from, an AGM one can be had from around £200 from pretty much anywhere.
If I do need to buy a new lithium ion battery, what kind do I need?
F series M cars use a 69ah battery and G series (including F90 M5) uses a 70ah battery.
The costs of these vary online, but the most expensive option is a brand new one from BMW
My car was in at a detailers for a week and after getting a call to say that my BMW display key was showing as being flat and that he was charging it (makes no difference to opening and starting the car, but he didn't know that), he asked if I could bring the spare when collecting it that morning. The message on the key was a red herring, he'd run the car battery flat, so we stuck it on charge at the points under the bonnet and I arranged to collect the next day as I didn't need the car anyway. This is when I made a few discoveries about LI batteries in cars and so when I went back to collect I wasn't hopeful that the battery would be charged. I was right.
Lithium Ion Batteries - Self Protection Relay
The battery has a voltage management system. In order to protect the battery cells, when the voltage on the battery drops to between 10 & 8 volts, an internal relay triggers that disconnects the battery cells, so that whatever is draining the battery is stopped from doing so. This means that even if you apply a charger to the points under the bonnet specified by BMW, it won't reach the battery or the electrical system on the car, as the connection is broken. I have read that if you're able to apply a positive charger connection and then a negative to what's called "true ground" this may work to jump-start the car but I didn't try it.
The only way to reset the self-protection relay is to apply 12 volts across the battery terminal on the battery itself.
But my alarm's going off, so it must have power?
No. The alarm system has it's own, separate battery, so if you think there's must be power going to the car because the alarm siren keeps sounding after you've opened the door with the key, think again!
How to charge the battery?
You need to get access to the battery itself, which on most modern BMWs is located in the boot. You have two options here. 1 is to apply a 12volt power supply to the battery to reset the self protection relay and then try the jump start terminals under the bonnet. Or use a proper lithium ion battery charger on the battery itself. This is what I did and after about 5 minutes, the electrical systems came back to life and I was able to start the car. I've now got it sitting charging up on my drive just to restore the battery,
Accessing the battery in the boot?
On the M5 the only way was to use the key blade to open one of the front doors and the crawl into the back. The rear doors won't unlock from the inside due to the deadlock system. I then pulled down the centre armrest, to get half way into the boot, where I was able to access the pull switches to fold the rear seat's down. That then gave me access to the battery under the boot floor. if you don't have folding rear seats or ski access in the centre, then you're out of the luck and you'll need to talk to a professional for advice on how to get to the battery. On the M5 there's no emergency trunk release as found on the M4 either.
Swapping out a Lithium Ion battery for an AGM one
If you're in a the position that your battery is knackered and needs to be replaced, it is possible to swap it our for an AGM battery. This will not disrupt or harm the electrical systems in the car contrary to what you may read online. As with any battery change there is a specific BMW Workshop application (ISTA) procedure for a battery swap and for changing from AGM to Lithium Ion and vice versa. This must be carried out due to the differences in how the two battery types are charged and maintained.
The only drawback from swapping from an LI battery to an AGM one is that the AGM won't last as long and is much heavier than the LI equivalent. But where as an LI battery from BMW will cost in the region of £1000+ depending on where you get it from, an AGM one can be had from around £200 from pretty much anywhere.
If I do need to buy a new lithium ion battery, what kind do I need?
F series M cars use a 69ah battery and G series (including F90 M5) uses a 70ah battery.
The costs of these vary online, but the most expensive option is a brand new one from BMW
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