Does anyone know the peak charging current of the 12V battery?

[wattmatters]

Why bother with anything other than a standard lead acid replacement? The car's charging system is set up for it.

 

[T1 Terry]

Why bother with anything other than a standard lead acid replacement? The car's charging system is set up for it.

The fact the lead acid battery has such a short life and after 2 yrs, you are at the mercy of the lead acid battery gods, just waiting for a cell to fail .... a 1 in 6 possibility or a battery made as cheap as possible having a cell fail .....

T1 Terry

 

[T1 Terry]

That's the dumbest thing i've ever heared. Why would you test a sealed battery at the cell terminals, bypassing the BMS? Nobody in practise will do that (why would they, they bought a battery, not a cellpack). So this was demonstration of the sealed product, not the cells themselfs.


Also if you bothered to read the comments, you might have cought this

"Update: just pulled 103Ah by charging to 16V and down to 4V! At least I pulled full capacity. "

So he did the proper test. But do you know of any 12V based inverters that work down to 4V? Most will die at ~10V.

So, that was very helpful to understand how you go about appraising a cell chemistry, not in the slightest, but rather depend on an influencer to push his bias and not bother to look at the information that influencer provided, like 17.2v would be fully 100%, after settling and actually measuring the cell voltages, not what he charged the pack to

If he bypassed the BMS to get the 16v you say he claims in in the "Update", then doesn't that destroy your opening reply
That's the dumbest thing i've ever heared. Why would you test a sealed battery at the cell terminals, bypassing the BMS?
At least other members will now know how much weight to apply to your battery capability assessments, and you have backed up my warning about drop in batteries

T1 Terry

 

[hojnikb]

So, that was very helpful to understand how you go about appraising a cell chemistry, not in the slightest, but rather depend on an influencer to push his bias and not bother to look at the information that influencer provided, like 17.2v would be fully 100%, after settling and actually measuring the cell voltages, not what he charged the pack to

If he bypassed the BMS to get the 16v you say he claims in in the "Update", then doesn't that destroy your opening reply
That's the dumbest thing i've ever heared. Why would you test a sealed battery at the cell terminals, bypassing the BMS?
At least other members will now know how much weight to apply to your battery capability assessments, and you have backed up my warning about drop in batteries

T1 Terry

Fact of the matter is; batery cant pull it's usable capacity with any of the standard equipment, unless especially designed around it.

The battery in question doesn't even have a properly setup BMS, so me, as an end user will never be able to pull full capacity, regardless of what equipment i have.

And to top it all off, the fundamental issue of charge/discharge efficiency and very wide voltage range (if you want full capacity) still stays.

So in the context of a car battery, this thing is pretty hopeless. You can't use full capacity, because you'll be cutoff at the top AND at the bottom. And i can't image how car's DCDC equipment would handle rough cutoff, if that was set lower than the charging voltage.
So in that regard, it's much worse than LFP.

Honestly, i'd rather trust an "influencer" that has proven to be reliable rather than some forum member, that can only back up it's statements with "i say it's like that so it must be true!"

 

[hojnikb]

The fact the lead acid battery has such a short life and after 2 yrs, you are at the mercy of the lead acid battery gods, just waiting for a cell to fail .... a 1 in 6 possibility or a battery made as cheap as possible having a cell fail .....

T1 Terry

Even if that were true (i run a 3 year old battery and it seems to be near perfect) you'd be still better off with an LFP based replacement. It's operating voltage is closer to lead acid, will offer more capacity for a given formfactor and will have plenty charge/discharge power for an EV application (again, it doesn't need to spin up an engine for it to require tons of peak amps).

I really don't understand why you brough Na+ in this discussion.

 

[T1 Terry]

Even if that were true (i run a 3 year old battery and it seems to be near perfect) you'd be still better off with an LFP based replacement. It's operating voltage is closer to lead acid, will offer more capacity for a given formfactor and will have plenty charge/discharge power for an EV application (again, it doesn't need to spin up an engine for it to require tons of peak amps).

I really don't understand why you brough Na+ in this discussion.

It could be that I actually work with off grid systems and have done for quite some time. I actually conduct hands on testing rather than form opinions from watching You Tube influencers ......

Knowledge is a two edged sword, a little is far more dangerous than none at all because it makes a person believe they actually know about a topic ......
A very common phrase uttered by many as their learning increases is a quote from Albert Einstein “The more I learn, the more I realize how much I didn't know'.”

T1 Terry

 

[hojnikb]

It could be that I actually work with off grid systems and have done for quite some time. I actually conduct hands on testing rather than form opinions from watching You Tube influencers ......

Knowledge is a two edged sword, a little is far more dangerous than none at all because it makes a person believe they actually know about a topic ......
A very common phrase uttered by many as their learning increases is a quote from Albert Einstein “The more I learn, the more I realize how much I didn't know'.”

T1 Terry

Exacly. So do i. Plenty of experience with LFPs and other chemistries. It's just a simple fact, that Na+ just isn't ready for primetim, unless you have a very specific application.

Cost isn't an advantage, Wh/kg or Wh/L or equipment compatability neither.

It might be a fun diy project, that doesn't care about cost or longterm viability.

If we go back on topic; OP needs a drop in replacement, not a science course. So it's simple matter of finding a LFP based battery with car terminals, that fits MG4.

 

[T1 Terry]

What ever you say, you might not always be right, but it does appear you can never be wrong .... good luck in life my friend, life is too short for this sort of nonsense

T1 Terry

 

[wattmatters]

The fact the lead acid battery has such a short life and after 2 yrs, you are at the mercy of the lead acid battery gods, just waiting for a cell to fail .... a 1 in 6 possibility or a battery made as cheap as possible having a cell fail .....

LFP and Na batteries have multiple cells that can fail too. Not sure what the number of cells has to do with anything. Same battery gods.

Lead acid is pretty robust, has proven its worth for over a century and if not abused it will last pretty well, and one just needs to swap it out on a reasonable schedule and use a decent brand.

If there is a well made drop in LFP, fine, provided it is set up to handle the charging system of a car expecting to work with a LA battery. Fortunately the voltages are similar enough it can work but the process of charging LFP is a little different as I'm sure you are well aware.

I had fun building a hybrid LFP - SLA battery for my last home - it takes some care to make sure operationally you get it right but it can be done.

Finally - the MG4 constantly gives us battery voltage data so we can readily assess its condition/health.

 

[wattmatters]

One of the really neat things about the MG4 (and other EVs) is that the auxiliary battery gets charged not only while driving but also while the car itself is being charged which for most EVs is pretty regularly. It also will use the drive battery to do an interim top up charge if necessary. So the aux battery is looked after pretty well.

 

[T1 Terry]

Lead acid has worked since it's inception in the 19th century. Built to the quality standards when lead acid was in it's prime, they would last a good 10 yrs.
At todays prices, that would be well over $1,000 and be hand built to be small enough to fit in the same lead acid battery position .... it would a flooded cell and require the same constant attention that such a battery requires to get the full cycle life ...... contaminate the electrolyte with tap water or let the electrolyte level drop to or below the level of the plates ..... there goes your cycle life

The same size no maintenance lead acid AGM battery built to a price as is todays norm. 2 yrs will be close to about it, you are gambling with failure past that point.

A drop in LFP or Na+ battery, with an active balancer and the ability to control the input current to ensure no cell goes over 3.65v ..... unobtainium .......
I can tell you how to build one to fit inside the original battery case and the electronics to mount outside the battery case, so it can ***dissipate any heat generated ....... but I have no plans to go back into the battery building business at the moment .....

T1 Terry

*** Heat generated and trapped inside the battery case will shorten the overall battery cycle life ...... heat kills any type of battery cell because the electrolyte will eventually boil and vent from the cell ..... only a flooded cell lead acid battery has an electrolyte replacement commonly available, pure water .....

 

[hojnikb]

You don't need an active balancer or current limiting on the BMS side. A passive balancer is just fine (and is part of most BMSes anyway), as for current limiting; given that LFPs tend to hold their current flat up to ~90-95%, there's no need for that either. You just cut off charging at 3.65V and its going to be fine. Maybe the battery won't be fully charged always, but that's actually a good thing in automotive application.

I think the biggest issue here is cold weather countries. If you're in an area that has regularly temps below freezing and if BMS is properly set, you might end up with a discharged battery eventually, since you can't charge it.

So a heated battery, sane voltage limits and a more relaxed short term discharge current limits would make such battery just fine for an EV application.
There's a chance such battery exists.