12 Volt Lithium Battery and Accessory Mode.

[Radioman]

Most people are afraid of new technology. Like I said, if it works for one year, it means it is treating it like a lead acid battery because of the built-in BMS in the Lithium iron battery. I had never have a problem starting the car since installed in hot or cold days so far. I will keep you guys posted every year or so if I still keep the car. My 2018 PHEV's 12KW lithium batteries are only giving me about 12-13 EV miles, not too happy about Mitsubishi's PHEV, may try a Toyota or Lexus PHEV next time.

You have to keep telling them… I think you make perfect sense and you first post said it all… some scan read too fast and don’t take it in…also agree many are scared of new but better technology

 

[DaveL59]

The issue is how the lithium battery behaves when its BMS decides it is fully charged. Does it go off-load to the charger circuit and so present an open circuit to the 12V converted in the car?

That potentially could induce either a fault condition to be logged in the control ECU or worse cause the charger to fail. Same issue in a regular ICE vehicle with a lithium battery being charged by the alternator, the regulator can fail because it sees a sudden open circuit.

You may get away with if for a while, but damned expensive if the worst happens.

Spontaneous combustion isn't as big a risk with LiFePO4 batteries but given the converter throws out 14.6v it'll push the LiFePO4 to full charge probably.

Now I have in fact replaced the lead AGM batteries in my UPSs but the charge voltage is set to float levels, so <28v for 2 12v in series. Hence those LiFePO4s never hit the full-charge state and after a couple months, no issues.

One way around the problem could be to add a small 12v AGM in parallel to the LiFePO4 so there will never be an open circuit condition. I've considered that since there's space to add something like a 7AH battery to do this. Not needing to try however since I replaced the OEM battery with an Optima AGM already.

A bit like that post about the handbrake, if yours has a manual one, sure, but circa 2016 they came with electric ones and you can't drive off without the seatbelt. Now you could get around that by pre-fitting the seatbelt and then sitting in the seat to fool it. Or you could modify the switch/sensor for it, but that's not what most people will/want to do - wonder if the MOT test will eventually pick up such a hack since it'd be clearly done to bypass safety systems the manufacturer put in place.

 

[yardbird]

Don't make the simple problem complicated. The BMS of the LiFePo4 battery is like a shut-off valve which will stop the charging current once it is full...period.

 

[DaveL59]

didn't say you shouldn't do it, by all means go for it, just do the research and understand the potential risks so you can't complain if it does happen and you're shelling out for some expensive repair work

As for 'it stops the charging current' - how? and what does the charger side see?

BMS's ain't created equal and as various reviews have shown, pre-made batteries ain't either. One here has done it and seems to have no issues a year+ later which is good to hear, but different markets may mean differing standards of battery build available. Hence do the research...