A few questions: if I understand your conclusions correctly from my thoroughly non-specialized POV, you are saying that this is a good way to both improve the performance and extend the life of existing lead installations?
Well, I'm not making any such claims. In principle this appears true but the devil is always in the details. And these devils tend to appear more frequently depending on how complex the system is and this system is trending towards increased complexity... especially with a mix of fundamentally different battery technologies.
However it seems like more and more people are becoming interested in this arrangement of LFP paralleled with LEAD so I thought I'd contribute with some test data 'for informational purposes'.
There are a number of pros and cons or 'concerns' that could be further discussed especially with respect to safety considerations and failure modes analysis.
If this is economically interesting given the installed base, are you saying it remains difficult to do with existing battery/management technology?
It's potentially interesting for sure, depending on one's circumstances, and this test just demonstrated that is wasn't difficult to do at all - i.e. it worked in the test environment with commodity 12V LFP batteries However, as seen above, there are ongoing concerns about how to best manage the LFP end-of-charge termination. Also I'd be concerned about what happens if one of a number of the lead cells became shorted - especially if it's an old battery as this could result in the lithium battery discharging into the lead bank and so on. Long story short batteries store significant energy and safety always needs to be a priority - which usually means following codes, using equipment for it's intended purposed and going easy on the 'experimentation' for permanent installations.
So what are you proposing?
Nothing really, it's simply an exploration to gather knowledge / experience and to better understand how these 12V LFP modules or blocks function in practice.
One interesting thing about the parallel lead bank is that it's completely insensitive to over voltage events and it can serve as a bit of a capacitor to snub high-voltage switching transients when the LFP 'protections' are activated or otherwise. For example, if I were on a sailboat in the middle of the ocean I would not want to be fully dependant on lithium batteries and I'd probably experiment with a parallel system with a LEAD, LFP or BOTH switch - as one the posters has suggested above.
It also gives one pause for thought about what an ideal 12V LFP building block would look like - i.e. what attributes or features it should have. Not for paralleling with lead in particular but rather just as a flexible, safe and robust 12V building block that is appropriate for a broad range of applications.
Also, more prosaically, how did you collect the data?
Yeah, the data comes from a number of precision zero-drift battery data loggers I personally built a few years ago. The white one on the wall is doing all kinds of 'AI' like estimations of the battery health, ongoing internal impedance assessment, high resolution data logging and so on. That big red battery has more than 6 years of 30sec logged data available. You can't design a good battery performance monitor w/o lots and lots and lots of field data to design around. I added another logger to measure just the LFP bank.
Last edited: