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 tale 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 seen 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 bother 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 every works for you.
A simple lead acid battery charger will be fine for charging them when/if needed.

I have used this company before https://osnpower.com/products/deep-...to-battery-solar-system-lto-battery-2-3v-55ah 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