I don't understand your question about idling.
@Dzl covered it, but I will flesh it out a bit to lay out my thinking.
My thinking was that if one is idling the vehicle to charge then a higher charge rate is likely a good economic move. Any theoretically-shorter battery cycle life would be offset by reduced wear/stress on the engine and alternator (auxilliary or otherwise).
If one is charging by multiple methods or if normal driving is sufficient to meet needs I am suggesting that lower charge rates increase LFP longevity. I understand this is not a universally-held position. Perhaps I am deluding myself and it is merely a form of Pascal's Wager.
I'm not aware of any downside to charging at 0.5C. The batteries can handle 1C, so 0.5C is already conservative. If you have references to such information, I'm all ears.
I suspect 0.5C is a compromise between charging speed and longevity. Joe Sixpack wouldn't be happy if his new $1000 battery took 5 hours to charge. OMG, that's like one of those lead-acid plebes!
![Stick out tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
So give them a rate high enough to keep them happy while making it through any warranty period.
I have seen manufacturers give the rated/warranted cycle life at 0.5C then give "and up to..." even higher cycle numbers with an asterisk ("when discharged 80% DoD and charged at 0.2C rates"). This isn't dispositive but it's food for thought.
Even more speculative: Battle Born says "We don’t recommend you exceed this [0.5C] charge rate as it can lead to a shortened battery cycle life." What is more likely, that 0.5C is a hard cutoff beyond which cycles will be reduced, or the top end of a sliding scale? More on this below.
Note: certainly not trying to tell you how to charge your bank. I am talking out loud about the factors that informed my own charging choices.
The BMS is temperature savvy, so if there were temperature ranges that needed less current then it would call for less power.
I looked over the the REC ACTIVE manual and website and didn't see any claims that it can regulate charging current from the alt beyond on/off. It was admittedly a cursory reading so maybe I missed something. You will certainly know more about it than I do.
It does kill the power at low temps close to freezing, as those charging at those temps can damage the battery.
It appears to be a sliding scale rather than hard cutoff -- see
these data sheets.
In the charts the average low temp at which 0.5C is allowed is 9.75C (49.55F) and the mean is 10C (50F). I hope I used those math terms right. The lowest of them is 5C (41F). Lower charging rates are allowed at somewhat lower temps, which might or might not tell us something about charging rates at warmer temps.
I like hot food and hot coffee and my heated mattress pad in the winter.
Same. Cooking and making coffee over a $40 stove allows me to run all my loads (including the heated mattress pad) on 100Ah LFP. I do
cook with electricity when there is excess solar power available which helps stretch the fuel supply. Right now I am cooking broccoli and cauliflower in a crock pot.
Ha, you should check out the Sprinter forum. We have guys there with 1100 AH lithium batteries running AC all day
Same on the Promaster and Transit fora. I fully support each vandweller building the rig that meets their particular wants and needs.
My own are minimal since there is no Wife Acceptance Factor and I follow mild weather. Once I had the van my total build cost was about $2250. I've been boondocking off-grid in it for the last (...checking...) 1,214 days. This low-cost approach allowed me to retire about 8 years early, so doggo and I are quite happy.
I was an early adopter of this technology for use in a van
Early adopters were DIYing LiFePO4 in vans by 2014-2015 (
example), leveraging information from the boating world that started showing up
in 2010-2011. In those days many people were running LFP "barefoot" because the BMS were so crude they were doing more harm than good. I am grateful the technology has advanced and come down in price.
Thank you for your thoughtful input.