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

[TheHypnoToad]

I'm looking to possibly replace my SLA 12V battery with a LiFePO4 version.

However some of these batteries have limited charging current, for example some of them can only charge at 50A.

Has anyone measured or does anyone know what the typical and max charging current is while the 12V battery is charging?

If I was to guess I'd say around 100A, and there are batteries LiFePO4 available that can handle this, but they tend to be heavier and more expensive.

 

[ReintjeWA]

I don’t have an exact answer for you but perhaps the people in this thread can help you out;

D

Thread '12 volt battery'

Nov 25, 2025

Hi there MG4 owners, I recently had a problem with my 12 volt battery and was quoted £180 by my local dealer for a replacement. I think it's got a bit more life left in it but want to be prepared to replace it. So does anyone know the correct model number or even a better replacement at a reasonable price. Thanks Dave.

• Davecut1
• 12-volt battery battery model battery replacement car battery dealer pricing mg4
• Replies: 18
• Forum: MG4 Upgrades & Accessories

 

[TheHypnoToad]

Hi, there's some good info in the thread you iinked, thanks for pointing me in the right direction

 

[T1 Terry]

I'm looking to possibly replace my SLA 12v battery with a LiFePO4 version.

However some of these batteries have limited charging current, for example some of them can only charge at 50A.

Has anyone measured or does anyone know what the typical and max charging current is while the 12V battery is charging?

If I was to guess I'd say around 100A, and there are batteries LiFePO4 available that can handle this, but they tend to be heavier and more expensive.

Just like lead, they don't make light weight lithium batteries. 100Ah of genuine 0.5CA (2C) capacity weighs 16kg, if they claim they have 100Ah lithium batteries that weigh less, then they are not genuine 100Ah batteries.

A Winston 4 cell in series 100Ah battery can be charged at up to 500A, (5C) but only to about 80% SOC charging that fast, the ability of the lithium ions to find somewhere vacant in the fingers of the graphite material starts to diminish rapidly above 80% SOC and continuing to force current in faster than it can find a spot in the graphite, will cause both the voltage a temperature of the electrolyte to climb rapidly, seriously damaging the cells ....
At 100amps (1C) you can charge the battery to 99% before the voltage will start to rise rapidly, but if you stop at 3.65V max in any cell, you will not do any harm to the battery or cells.

If you are looking at a drop in battery and it is limited to 50 amps charging acceptance, leave it on the shelf, the limitation is the bicycle battery capacity BMS (Battery Management System) and quite likely, a battery that is only a genuine 50Ah capacity.

If you want a battery you can rely on, build it yourself, it's really not that hard and you will know exactly what is in it, you can access all the parts and replace anything that might need replacing, and you can transfer it to your next car, or take it camping for a power supply ..... what ever you might use a 12V battery for, it would be available to use.

T1 Terry

 

[TheHypnoToad]

Thanks for the info, that's really helpful.

I think I'll go the DIY route, I'm currently looking at places that sell Sodium Ion cells, so far I've found 75Ah cells that seem good, they can be discharged at 3C continious so I think this should be plenty.

I'll also look to include a balance cable that's accessable as I already have a charger that can balance charge and supports LFP cells, so I hope I can use this on the sodium ion cells.

As sodium ion cells are pretty new, a lot of my local battery sellers do not seem to have them, so I may need to use AliExpess, which isn't ideal!

 

[T1 Terry]

Be aware, sodium ion cells have limitation of how fast you can charge them, 1C is the accepted limit, but they have a higher max cell voltage of just over 4V per cell, so plenty of overhead for voltage creep when charging faster for shorter periods.
The other option is LTO cells, but you would need 5 cells to cope with the 14.4V charging. The up side is, they can handle 10C in both directions, so a 5 x 50Ah cell battery could handle 500 amps charging and discharging.
6 x 50Ah cells would give you a lot of head room for fast charging, but 14.4V would only be a 50% SOC, so 25Ah capacity, plenty for an MG4 aux battery and it would last long enough to will to your grandchildren, just not a lot of capacity for an aux battery for camping etc .....

I would recommend a HA03 8 cell balance and just leave 2 cells (4 wires) with the insulation covers still protecting the terminals .... or you could double up the first two cell connection and the last two ..... which ever works for you.
A simple lead acid battery charger will be fine for charging them when/if needed.

I have used this company before Deep Cycle YINLONG Lithium Titanate Battery Lto CELL 55Ah LTO Battery but it seems my contact there, Dinah, isn't there or isn't in sales anymore. I can vouch for Dinah and her reliability, but she is the only one I have ever dealt with, so I can't necessarily vouch for anyone else there.

They were happy to either just supply the parts, or build the battery ready for you .... up to you.

T1 Terry

 

[hojnikb]

Sodium ion is crap in almost every way compared to LFP. And they ain't even cheaper than LFP, so no cost benefit either.


I'd say there's no chance the onboard charger is charging the battery at 50A. Being that onboard battery is a ~50Ah lead acid unit, it's highly unlikely that it can take more than ~15-20A of peak charging current when empty. Lead acid simply can't charge very fast.

So any LFP pack designed for automotive use would be ok. Just make sure that it has undertemparature charging protection.

 

[hojnikb]

Just like lead, they don't make light weight lithium batteries. 100Ah of genuine 0.5CA (2C) capacity weighs 16kg, if they claim they have 100Ah lithium batteries that weigh less, then they are not genuine 100Ah batteries.

A Winston 4 cell in series 100Ah battery can be charged at up to 500A, (5C) but only to about 80% SOC charging that fast, the ability of the lithium ions to find somewhere vacant in the fingers of the graphite material starts to diminish rapidly above 80% SOC and continuing to force current in faster than it can find a spot in the graphite, will cause both the voltage a temperature of the electrolyte to climb rapidly, seriously damaging the cells ....
At 100amps (1C) you can charge the battery to 99% before the voltage will start to rise rapidly, but if you stop at 3.65v max in any cell, you will not do any harm to the battery or cells.

If you are looking at a drop in battery and it is limited to 50 amps charging acceptance, leave it on the shelf, the limitation is the bicycle battery capacity BMS (Battery Management System) and quite likely, a battery that is only a genuine 50Ah capacity.

If you want a battery you can rely on, build it yourself, it's really not that hard and you will know exactly what is in it, you can access all the parts and replace anything that might need replacing, and you can transfer it to your next car, or tale it camping for a power supply ..... what ever you might use a 12v battery for, it would be available to use

T1 Terry

Most 100Ah 12V LFP batteries are under 10 kilos and are true 100Ah (usually 103-107Ah when new). Lead acid will be at least 30-35 kilos for that nominal capacity. If you include the 50% DoD for safe cycling, that weight goes up to 70+ kilos. If you include additional capacity (since lead acid is usually rated at C/20 or even C/100) needed to hit that kWh at C/2 (as LFP is usually rated for), then the weight to usable capacity is even worse.

Lead acid is truly terrible in terms of weight/kWh.

 

[T1 Terry]

Most 100Ah 12V LFP batteries are under 10 kilos and are true 100Ah (usually 103-107Ah when new). Lead acid will be at least 30-35kilos for that nominal capacity. If you include the 50% DoD for safe cycling, that weigh goes up to 70+ kilos. If you include additional capacity (since lead acid is usually rated at C/20 or even C/100) needed to hit that kWh at C/2 (as LFP is usually rated for) then weight to usable capacity is even worse.

Lead acid is truly terrible in terms of weight/kwh

Don't want to start an argument here, but by the time a proper BMS, separate active balancer, strapping for prismatic cells, terminal bolts and links
A true C2 rated Prismatic100Ah LFP battery weighs 16kg, the cells alone weigh 3.7kg for a 100Ah 3.2v nom. cell, 4 cells weigh 14.8kg

Cylindrical cells are lighter, but there is a trade off in their ability to accept high rate charging, even pulse charging they are limited to 1.5C on a 30 sec 50/50 cycle at bulk charging rate, not a lot of use as an aux replacement battery.

LTO is the better option if going for cylindrical cells, 50Ah cells weigh roughly 2kg x 10 to build a 12v nom. 100Ah battery, 20kg, then all the building blocks, 2 per cell, links, nuts and washers, BMS and active balancer, then a case around it because both ends are live, you are approaching the weight of a 100Ah C20 rated lead acid deep cycle AGM battery. The benefits are, up to 10C charging and discharging rates, very little heat generation and a 30,000 cycle life from 100% SOC to 0% SOC, 82 yrs if you fully discharged them every day .... as I mentioned before, a battery to leave in your will to your grandchildren

T1 Terry

 

[T1 Terry]

Sodium ion is crap in almost every way compared to LFP. And they ain't even cheaper than LFP, so no cost benefit either.


I'd say there's no chance the onboard charger is charging the battery at 50A. Being that onboard battery is a ~50Ah lead acid unit, it's highly unlikely that it can take more than ~15-20A of peak charging current when empty. Lead acid simply can't charge very fast.

So any LFP pack designed for automotive use would be ok. Just make sure that it has undertemparature charging protection.

Possibly a limited understanding of how these DC to DC chargers work. They have a max current output and a controlled maximum voltage. If the DC to DC can supply 50 amps, it will, until the terminal voltage reaches 14.4V.
The fact a lead acid battery can only accept a much slower charge rate, means the 50 amps brings the terminal voltage up to 14.4V very quickly, the amps then drop to what ever will maintain that 14.4V .......

So, an LFP, LTO and Na+ battery will accept as much current as can be supplied, until the voltage increases to 14.4V .....

You need to do a lot more research on Na+ batteries, your opinion about them is based on 2 yr old at minimum data, look at the new CATL Na+ cells, their specs and expected life cycle, then come back and give a 2026 data opinion.

T1 Terry

 

[hojnikb]

Don't want to start an argument here, but by the time a proper BMS, separate active balancer, strapping for prismatic cells, terminal bolts and links
A true C2 rated Prismatic100Ah LFP battery weighs 16kg, the cells alone weigh 3.7kg for a 100Ah 3.2v nom. cell, 4 cells weigh 14.8kg

Cylindrical cells are lighter, but there is a trade off in their ability to accept high rate charging, even pulse charging they are limited to 1.5C on a 30 sec 50/50 cycle at bulk charging rate, not a lot of use as an aux replacement battery.

LTO is the better option if going for cylindrical cells, 50Ah cells weigh roughly 2kg x 10 to build a 12v nom. 100Ah battery, 20kg, then all the building blocks, 2 per cell, links, nuts and washers, BMS and active balancer, then a case around it because both ends are live, you are approaching the weight of a 100Ah C20 rated lead acid deep cycle AGM battery. The benefits are, up to 10C charging and discharging rates, very little heat generation and a 30,000 cycle life from 100% SOC to 0% SOC, 82 yrs if you fully discharged them every day .... as I mentioned before, a battery to leave in your will to your grandchildren

T1 Terry

https://www.amazon.de/-/en/WattCycle-Bluetooth-Monitoring-Discharge-Motorhome/dp/B0DT4J3PKP?crid=3G3OCQ8WTHM82&dib=eyJ2IjoiMSJ9.gK4uA4Bb9hqene7psRx_vaGvi_t3MAQeNLR1Yw9PX0TcS_AYEYkHclmQuPCT2_ymeu9ijEE85Xg1uQjfOKavDShm_Xa1gDM5fHN8iAzi4RahhJ8XHHZGA2K1_0CM8O5j5T7XSUbxGU0QAixFhvC2srdhml9zVOCB_nf6c-xreVMvF1-N3MQbkRyjO0Xtse1sqLIfM2ITj_NkPXgI9YmbPZtMzv3WsRbLTlGpFr6ReoBz-seT0zMSix5xRPhXAj6uOQv9VYq8L-idccOPUlQy5d0JtqZ085E8dH453sny7W4.LLZ6wlsB-2_Ct2oplvDP1D3qdH72bxnkwZaAQSHUsJ4&dib_tag=se&keywords=wattcycle&qid=1767679765&sprefix=wattcycle%2Caps%2C145&sr=8-5&th=1

9.3kg, will do rated capacity at C/2 easily and you can discharge/charge at 100A continuous.

While these are not meant for starter batteries (due to their 100A BMS) they will happily handle an EV. There's no engine to start or very heavy loads on the 12V, so 100A is plenty enough for this sort of purpose.

 

[hojnikb]

Possibly a limited understanding of how these DC to DC chargers work. They have a max current output and a controlled maximum voltage. If the DC to DC can supply 50 amps, it will, until the terminal voltage reaches 14.4v.
The fact a lead acid battery can only accept a much slower charge rate, means the 50 amps brings the terminal voltage up to 14.4v very quickly, the amps then drop to what ever will maintain that 14.4v .......

So, an LFP, LTO and Na+ battery will accept as much current as can be supplied, until the voltage increases to 14.4v .....

You need to do a lot more research on Na+ batteries, your opinion about them is based on 2 yr old at minimum data, look at the new CATL Na+ cells, their specs and expected life cycle, then come back and give a 2026 data opinion

T1 Terry

If the DCDC charger is designed with any safety in mind, it will have current limits, so that it won't cook that stock 50Ah lead acid battery. Terminal voltage is just part of that.

Your logic would work with an old car with alternator charging the battery directly. In that case, alternator will try to output all it's power to hit that maximum voltage.

As for Na+ batteries. As long as there's no cells or packs with better quality cells, that can be bought by end users, my opinion stays. Fact of the matter is, even new cells have wide voltage range (which you don't want), very low charge/discharge efficiency and even lower energy density compared to LFP. Unless they're alot cheaper than LFP, they make absolutly no sense.

Will said it best

 

[T1 Terry]

https://www.amazon.de/-/en/WattCycle-Bluetooth-Monitoring-Discharge-Motorhome/dp/B0DT4J3PKP?crid=3G3OCQ8WTHM82&dib=eyJ2IjoiMSJ9.gK4uA4Bb9hqene7psRx_vaGvi_t3MAQeNLR1Yw9PX0TcS_AYEYkHclmQuPCT2_ymeu9ijEE85Xg1uQjfOKavDShm_Xa1gDM5fHN8iAzi4RahhJ8XHHZGA2K1_0CM8O5j5T7XSUbxGU0QAixFhvC2srdhml9zVOCB_nf6c-xreVMvF1-N3MQbkRyjO0Xtse1sqLIfM2ITj_NkPXgI9YmbPZtMzv3WsRbLTlGpFr6ReoBz-seT0zMSix5xRPhXAj6uOQv9VYq8L-idccOPUlQy5d0JtqZ085E8dH453sny7W4.LLZ6wlsB-2_Ct2oplvDP1D3qdH72bxnkwZaAQSHUsJ4&dib_tag=se&keywords=wattcycle&qid=1767679765&sprefix=wattcycle%2Caps%2C145&sr=8-5&th=1

9.3KGs, will do rated capacity at C/2 easily and you can discharge/charge at 100A continuous.

While these are not meant for starter batteries (due to their 100A BMS) they will happily handle an EV. There's no engine to start or very heavy loads on the 12V, so 100A is plenty enough for this sort of purpose.

Are you saying these batteries are something you have tested over a long period to verify what you claim?
The temp claims don't look terribly realistic or believable, but maybe there is something lost in translation ....

Here is a video that might help you with your myth understanding of Na+ chemistry batteries

T1 Terry

 

[hojnikb]

Are you saying these batteries are something you have tested over a long period to verify what you claim?
The temp claims don't look terribly realistic or believable, but maybe there is something lost in translation ....

Here is a video that might help you with your myth understanding of Na+ chemistry batteries

T1 Terry

Wattcycle batteries have been pretty well tested by now and very often the recommeded budget battery in the LFP world. And not that -25C is that unreasonable for LFP batteries. It's the charge rate, that doesn't exist below 0C. You can still discharge it, albeit with reduced power.

I'm not going to look at bullshit videos, regurgitating marketing materials. Show me real cells,in retail products, that performe even close to what they claim.

It's pretty much every week, that there's a new breakthrough in battery tech. It's the mass production and cost efficiency that's actually interesting to us.

 

[T1 Terry]

Wattcycle batteries have been pretty well tested by now and very often the recommeded budget battery in the LFP world. And not that -25C is that unreasonable for LFP batteries. It's the charge rate, that doesn't exist below 0C. You can still discharge it, albeit with reduced power.

I'm not going to look at bullshit videos, regurgitating marketing materials. Show me real cells,in retail products, that performe even close to what they claim.

It's pretty much every week, that there's a new breakthrough in battery tech. It's the mass production and cost efficiency that's actually interesting to us.

The expected reply, CATL are a small player and EV manufacturers have no idea of what they really need

I actually use Na+ 200Ah cells in 3P4S configuration in my motorhome, that is actually our house until our house is rebuilt after being burnt to the ground.
They have performed faultlessly for the last 12 mths, 24/7, powering a 5kVA Victron Multiplus II as well as all the 12V loads .... and acts as the back up start battery if the lead acid unit isn't up to the task of spinning over the V10 6.8 ltr engine ......

I've been doing this sort of thing for the last 15 yrs, had a slave labour position at my wife's business T1 lithium, I have actually carried out all the testing hands on so I'm confident to back what I say .....

T1 Terry

 

[hojnikb]

The expected reply, CATL are a small player and EV manufacturers have no idea of what they really need

I actually use Na+ 200Ah cells in 3P4S configuration in my motorhome, that is actually our house until our house is rebuilt after being burnt to the ground.
They have performed faultlessly for the last 12 mths, 24/7, powering a 5kva Victron Multiplus II as well as all the 12v loads .... and acts as the back up start battery if the lead acid unit isn't up to the task of spinning over the V10 6.8 ltr engine ......

I've been doing this sort of thing for the last 15 yrs, had a slave labour position at my wife's business T1 lithium, I have actually carried out all the testing hands on so I'm confident to back what I say .....

T1 Terry

So you can tell us what kind of usable capacity you get out of those 200Ah cells, how much power you can pull from them close to 0% SOC and how high is your charge/discharge efficiency?
Oh and what kind of degradation you're getting after 12mths.

Of course CATL is a big player, everyone knows that. But their marketing sometimes is pretty wild. They're Chinese after all and until we see actual mass produced products, i'll take their marketing with a big grain of salt.

 

[T1 Terry]

So you can tell us what kind of usable capacity you get out of those 200Ah cells, how much power you can pull from them close to 0% SOC and how high is your charge/discharge efficiency?
Oh and what kind of degradation you're getting after 12mths.

Of course CATL is a big player, everyone knows that. But their marketing sometimes is pretty wild. They're Chinese after all and until we see actual mass produced products, i'll take their marketing with a big grain of salt.

Manufacturers do place production orders on hype and spin.

As far as degradation, 12 mths is way too early to tell, they are delivering 1C down to around 20% SOC and holding 11.8v while delivering it, so they are doing ok at the moment .... but time will tell.
I have Winston LYP cell systems now in their 11th and 12 yrs, still working 24/7 in off grid houses ...... how they are treated is half the battle, but you have to start with quality to get good results

T1 Terry

 

[hojnikb]

My home LFP setup, consisting of 16S 280Ah cells (grade A-, since those were they cheapest i could source) still hold near full capacity after roughly 300 cycles. They did degrade initially to about 97-96%, but are still holding that after many cycles. And this pack is heavily abused; being fully charged and near fully discharged every day in sunny days (ie when solar producton is high). And charged to 3.45V/cell. And no compression either or cooling.

And unlike Na+, they hold their power and voltage down to 5% SOC, before voltage starts dropping. As is typical of LFPs.

From what i've seen, most comercially available Na+ cells or packs seems to be pretty terrible. From poor capacity if not drain to ~1.5-2V per cell (which limits the inverter availability, especially cheap ones) to atrocious charge/discharge efficiency (i've seen as low as 60-70%, which is even worse than lead acid) to premature faulires and high degradation.

Given the dirt cheap cost of LFPs, very good BMS support and being pretty well tested in the field, i see no reason to use anything else for ESS. Even if Na+ costed the same; it would still be more expensive to build an entire system around their limitations.

 

[T1 Terry]

If the DCDC charger is designed with any safety in mind, it will have current limits, so that it won't cook that stock 50Ah lead acid battery. Terminal voltage is just part of that.

Your logic would work with an old car with alternator charging the battery directly. In that case, alternator will try to output all it's power to hit that maximum voltage.

As for Na+ batteries. As long as there's no cells or packs with better quality cells, that can be bought by end users, my opinion stays. Fact of the matter is, even new cells have wide voltage range (which you don't want), very low charge/discharge efficiency and even lower energy density compared to LFP. Unless they're alot cheaper than LFP, they make absolutly no sense.

Will said it best

This bloke should at least do a bit of research.
First thing obvious, they are using an LFP BMS, that explains why it wouldn't charge at a low terminal voltage, but if he was doing a non bias test, he would have charged at the cell terminals, not the BMS terminals.
The fact it cut out at 14.5v says LFP, Na+ is 4.3v per cell, so truly full would be 17.2v.
A copy of the comment I just posted, let's see how long it last before he deletes it

@T1Terry37​

0 seconds ago
You should do a bit of research on a product before you let your mouth make a fool of you
.Na+ fully charged is 4.3v rested per cell, 4 cells, 17.2v. The chart you show in the beginning tells you that, yet you didn't read it?
With this sort of background knowledge, you could have proudly announced that the drop in battery had an LFP BMS and not an Na+ BMS.
The fact you half charged the cells, allowing for voltage settling of a never condition charged battery, then discharged it to an average of 2.5v per cell, again, looking at your chart, around 15% SOC ...... giving you a huge benefit of the doubt here, you went from 65% SOC down to 15% SOC, you pulled 50% capacity (65%SOC - 15% SOC = 50%) 64Ah from a non balanced pack @ 1C ...... You absolutely gave Na+ (Sodium ion) and incredible review putting them well ahead of any drop in battery test I've seen so far.T1 Terry

I would have thought you would have picked up on the bits I just pointed out ..... the info was there to see

T1 Terry

 

[hojnikb]

This bloke should at least do a bit of research.
First thing obvious, they are using an LFP BMS, that explains why it wouldn't charge at a low terminal voltage, but if he was doing a non bias test, he would have charged at the cell terminals, not the BMS terminals.
The fact it cut out at 14.5v says LFP, Na+ is 4.3v per cell, so truly full would be 17.2v.
A copy of the comment I just posted, let's see how long it last before he deletes it

@T1Terry37​

0 seconds ago
You should do a bit of research on a product before you let your mouth make a fool of you
.Na+ fully charged is 4.3v rested per cell, 4 cells, 17.2v. The chart you show in the beginning tells you that, yet you didn't read it?
With this sort of background knowledge, you could have proudly announced that the drop in battery had an LFP BMS and not an Na+ BMS.
The fact you half charged the cells, allowing for voltage settling of a never condition charged battery, then discharged it to an average of 2.5v per cell, again, looking at your chart, around 15% SOC ...... giving you a huge benefit of the doubt here, you went from 65% SOC down to 15% SOC, you pulled 50% capacity (65%SOC - 15% SOC = 50%) 64Ah from a non balanced pack @ 1C ...... You absolutely gave Na+ (Sodium ion) and incredible review putting them well ahead of any drop in battery test I've seen so far.T1 Terry

I would have thought you would have picked up on the bits I just pointed out ..... the info was there to see

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.