How to keep 12V aux battery charged..?

Good morning, friends. I believe that most (all?) EVs have a separate state 12V circuit/battery separate from the LI battery which powers the Electric propulsion motor. It's my understanding that if this smaller battery somehow goes flat, it's impossible to start the CE-04.

Harley LiveWire owners tell many tales of discharged 12V batteries and lack of parts leaving them starmed.

this said, does anyone know how the battery on our scooters is kept charged, or how to charge it separate from the main pattern pack?
thank,you!

Hiya,

I guess you're right about the necessity for the 12V battery being adequately charged to start the CE 04 but I've heard no reports about faulty batteries and I'm confident that BMW have engineered a decent system to maintain 12V battery health so I'm not worried. I've had no issues at all with the 12V battery on my CE 04 since I got it in April 2022 although the longest I've gone without using or charging my CE 04 has been about two weeks.

Regarding your second from last question, there was a thread about this last year, here's a link:

Advice please long term storage...

Although I haven't tried it, the user manual notes that the 12V battery can be charged via the accessory socket using an approved charger. I have successfully used an Optimate 4 (CAN-bus edition) with my new C400GT and my recently-sold R1200R for trickle charging. Note that the CE 04 manual states that a completely flat 12V battery would need to be disconnected and charged externally which is just a matter of removing the rear panel on the right-hand side, taking out the battery and charging it with a conventional lead acid motorcycle battery charger at an appropriate current. As an aside, my Optimate 4 can be switched out of CAN-bus mode for this purpose.

So I have a trickle charge that I plug to the bike, just to be on the safe side.

I have an MV that won't start fi it is not completely charged, so I am very diligent in connecting the CE04.

The LI battery also check the state of the charge of the 12v battery and charges it when needed.

interesting, my CE 04 12v battery went completely dead on Friday. No issues of any kind the previous days prior to this even. I had the bIke towed via AAA and was told specifically that in fact the 12v battery had died, I always have kept the scooter 100% plugged into my bike. Was the told the battery connections had come loose and therefore was now completely dead. unfortunately it’s going to take about 2weeks to recieve a new 12v battery. The good news it’s all under warrant.

As per the manual, as long as the traction battery has a state of charge over 20% or is plugged into a charger, the bike will wake up the electronics and check the status of the 12V battery every 2 days and charge the battery using the onboard DC-DC converter if necessary. No need to use a seperate battery tender or anything like that. That's why BMW warns if you are going to park the bike for extended periods to charge the traction battery to at least 50% state of charge, to enable the automatic 12V battery maintenance to take place.

According to BMW you never have to charge the 12 volt battery The reason is the bikes processor looks at the 12 volt batteries voltage each day and charges it accordingly or when needed. This charging happens automatically without user input. This does not require the bike to be plugged in or charging. Also be aware that you should never charge the 12 volt battery without first disconnecting it from the bikes circuity . The reason is - your charger is applying current and voltage to the bikes DC to DC charger circuit at the same time which is not advisable. If your charger is applying a charge when the high voltage battery is charging the 12 volt battery, you can easily damage the DC to DC down converter charger which takes the high voltage from the bikes drive battery and down converts it to 14-16 volts to charge the 12 volt battery.

Ride Safe - Mike

Have new CE 04 and dead as a door nail this morning. Having half a clue, I disconnect 12 volt battery and tested - read less than 5 volts, but charged up okay. Not happy as was running out door to go to appointment. Surely the bikes big battery must not have changed it as BMW states it does. Should I trust the 12 volter again or go get a new one from dealer?
Merv from Melbourne

Merv said:

Have new CE 04 and dead as a door nail this morning. Having half a clue, I disconnect 12 volt battery and tested - read less than 5 volts, but charged up okay. Not happy as was running out door to go to appointment. Surely the bikes big battery must not have changed it as BMW states it does. Should I trust the 12 volter again or go get a new one from dealer?
Merv from Melbourne

Click to expand...

Hello Merv.
BazT. Gosport UK.

Thanks BazT,
After charge up of 12v, no more issues in last day. Keep an eye on and go back to dealer if issue repeats. Just part of the education process with EVs I think. Had it 6 weeks and otherwise love it and is my favourite ride over my GS Adventure too!

Cheers,
Merv

Thanks everybody for all of the advice. I've only had my CE 04 for a few weeks. I'm planning to keep the T25 driver and 8mm socket driver handy if I ever need to get to the 12V battery (including battery cable connections) when I'm out with the scooter.

If the 12V battery was totally flat, wouldn't it mean that the electronically latched helmet compartment and phone compartment could not be opened until 12V power was restored? Have to think about where the tools and my phone are kept in case this were to happen.

pedalmike. Great minds think alike. If you pull the front fairing cover downward it opens and there is a T25 and Philips head strapped into position behind on bike (in Australian delivered bike anyway). You will see when you open. I immediately thought the same. Even of leaving a T25 in the non locking charge point void, but not smart for bike security I guess. I found instructions in manual re access to get to tools. And you’re right, no access to locking phone compartment or side locker. Also if you had steering locked, you can’t unlock it which means whole world of hurt trying to move, if even onto a trailer.

Merv- thanks so much for your post! I pulled down the fairing cover and found the T25 wrench...alas no Phillips screwdriver in North America!

Hadn't used the bike for quite a few weeks and when I started it, a big, frightening orange panel lit up saying battery critical - proceed immediately to charging station or something along those lines. I put it on charge but it was already 50% full, so imagine it was a 12V battery problem - anyway after charging a bit it and riding into town (2 miles or so) it was OK again.