OK to charge CE 04 12V using Optmimate 4 CANBUS through accessory socket?

[pedalmike]

Hi. Wondering if anyone has experience using one of the Optimate CANBUS-compatible 12V trickle chargers through the CE 04 accessory outlet. My scooter will be garaged in Arizona for several months this summer while I'm not there. Advice I am getting for traction battery longevity is to leave it at roughly a 30% state of charge, and put the 12V battery on a trickle charger. If the Optimate 4 CANBUS works with the CE 04, I can just plug it into the accessory socket and leave it. Rep from Tecmate in the US says the charger will work with the CE 04.

 

[Bob66]

If I were laying up my CE 04 for 3 months I would charge to about 80% and leave it to look after itself.

I would never by choice leave my beloved CE 04 at 30% for any significant length of time. Here's what BMW says in the CE 04 owners handbook: "Do not leave the E-Scooter out of use for a lengthy period with the high- voltage battery in a low state of charge. Before leaving the vehicle out of use for a lengthy period, check the charge status indicator and make sure that the high-voltage battery is fully charged. Excessive deep discharge will damage the high- voltage battery."

Current wisdom says that for maximum longevity a NMC Li-ion battery should be kept in a state of charge as close as possible to 50% so if I were to store my bike for 3 months I would aim to start significantly above 50% to allow the CE 04 sufficient energy reserves to run its operating system and trickle charge the 12 V battery without dipping much below 50% charge.

I have an Optimate-4 CANBUS Edition charger for my ICE bikes which I can confirm works with my CE 04 but I don't see the need for it given that the energy capacity of the propulsion battery is more than 100 times that of the 12 V battery (8500 Wh versus 60 Wh ). For peace of mind, I'm sure it will be fine to use an Optimate-4 CANBUS Edition though.

 

[Bob66]

Further to my previous post, I note that the owner's handbook for the CE 02 gives different advice on battery care :

"Recommendations for care of the traction battery
To ensure optimum utilisation and service life of the traction battery, follow the recommendations set out below:
Immediately recharge a discharged traction battery
Optimum state of charge for the eParkourer when in regular use is between 20 % and 80 %.
During a long stationary period of the eParkourer, for example in winter, maintain the state of charge between 30 % and 50 %.
Optimum ambient temperature during prolonged storage of the eParkourer is between 0 °C and 25 °C."

I'm not sure why there is a difference between the CE 02 and CE 04 long-term storage advice - could the battery chemistries be different?

 

[pedalmike]

Bob66- Thank you for your thoughtful replies. I have been thinking along the same lines as you until I watched this Engineering Explained video that discussed optimum storage conditions for a Li-ion NMC battery pack

In my situation, the temps in my garage will exceed 25 degrees C....and could approach 40C. I realize the video is not about the CE 04 in particular, but it is the same battery chemistry. The video suggests that if the storage conditions are in warmer temperatures, the battery will benefit from from a state of charge in the neighborhood of 30%. If 30% is optimum, I didn't want to risk having the traction battery only topping off the 12V battery for several months.

From what I can read, it appears that the CE 02 battery chemistry, is the same as CE 04, but it has (2) 1.96 kWH packs vs. our single 8.9 kWH (8.5 usable) pack. Also, it appears that the CE 02 is packs are air cooled only while the CE 04 pack is air and liquid cooled.

It's interesting that BMW advises the optimum battery SOC in regular use is 20-80%. I would like to have a target SOC setting for the CE 04 at 80% for everyday use, then bring it to 100% when needed for a longer journey. I wonder if a future software update could provide us with that capability.

Bob66, if you or others in the group think I am reaching the wrong conclusion here, I'd like to hear that.

 

[Bob66]

Pedalmike - I'm no battery expert so most of my knowledge comes from YouTube. I have seen that video before and it all made intuitive sense to me.

I note that the video looks scary with respect to the impact of SOC on rate of degradation of battery capacity at 50ºC. In your situation I would probably store my CE04 at an indicated charge level of maybe 50% - 55% but that would be just based on the gut instinct of trying to balance the distribution of lithium evenly between anode and cathode. However, before leaving your CE 04 unattended for 3 months, it might be advisable to test out the battery maintenance system and condition of the 12V battery by leaving the CE 04 dormant for a shorter term - say two or three weeks - to get a rough idea of how much SOC you will lose per week. If you're going to use an Optimate 4 then I suggest that you try it out over a few weeks of dormancy just to check that no confusions occur between bike and Optimate when the CE 04 12V battery maintenance process kicks in. I only tried my Optimate 4 for a few minutes just to check that it communicated with my bike and initiated a charge.

I still don't understand why BMW doesn't allow control of SoC from the bike. I can only assume that they are confident that always charging to 100% doesn't have any significant effect on battery life due to how good their battery and battery management system is. My method of least-painfully managing SOC day-to-day is to use a simple countdown timer plug socket with the supplied BMW charger. I have one that, with each press of a button, increments the time that the switch is on for. At 6A charging current and up to 80% SOC the charging rate is a bit below 20% SOC per hour.

 

[pedalmike]

Bob66- many thanks for your additional thoughts. Your advice makes good sense to me....I'll take it into consideration!

Similar to your approach, I have my supplied BMW traction battery charger plugged into a Kasa brand smart outlet. I can control the outlet remotely, schedule any duration of charging time I specify, etc. Periodically, I've been able to have the BMW Connected app show me state of charge on my phone in real time, but after awhile it seems to display SOC from an earlier time (i.e. 20 mins ago, an hour ago). I don't understand how to refresh the connection...perhaps if I'm connected via WiFi vs Bluetooth directly from the scooter, that's the difference?