Replacing MG ZS EV 12V lead acid with Lithium Phosphate battery (LiFePo4)

[mlsaksiri]

After 2+ years, my MG ZS EV 12V battery died. Rather than replacing it with
a lead acid battery, I decided to go for a LiFePo4 or Lithium Phosphate
battery. After the battery died, I jumped with a smaller LiFePo4 battery and it
came back to life. So I was pretty sure that it would work. Plus I have
already been replacing my UPS lead acid batteries with LiFeP04 for more
than 2 years and have had no problems. Details of how-to are attached as pdf.

 

[Deleted member 823]

A useful post, thanks for sharing. I've moved it to the ZS section of the fourm

 

[MartinSEsr]

After 2+ years, my MG ZS EV 12v battery died. Rather than replacing it with
a lead acid battery, I decided to go for a LiFePo4 or Lithium Phosphate
battery. After the battery died, I jumped with a smaller LiFePo4 battery and it
came back to life. So I was pretty sure that it would work. Plus I have
already been replacing my UPS lead acid batteries with LiFeP04 for more
than 2 years and have had no problems. Details of how-to are attached as pdf.

Could you say how much a replacement lead acid battery would have been, and how much the LifPo batter was, please? Thanks.

 

[mlsaksiri]

Here, a reasonable 12V lead acid battery costs about 100 USD. Some brands may charge as much as 200 USD. This price usually includes a home replacement service performed by one of the battery shop's motorcycle mechanics for obvious reasons. The Lithium Phosphate battery I bought cost 150 USD.

 

[ZiggyStandard]

After 2+ years, my MG ZS EV 12v battery died. Rather than replacing it with
a lead acid battery, I decided to go for a LiFePo4 or Lithium Phosphate
battery. After the battery died, I jumped with a smaller LiFePo4 battery and it
came back to life. So I was pretty sure that it would work. Plus I have
already been replacing my UPS lead acid batteries with LiFeP04 for more
than 2 years and have had no problems. Details of how-to are attached as pdf.

Thanks for posting this, it helped enormously with my replacement.

 

[sproglett]

really insteresting thanks, i have 2 questions,
a) what is the current rating needed for the BMS or the maximum load the MG takes from the 12V battery, i believe the heater comes from it
b) what happens if it gets cold, some lifepo4 batteries dont like the cold

 

[Bricktop X PWR]

really insteresting thanks, i have 2 questions,
a) what is the current rating needed for the BMS or the maximum load the MG takes from the 12V battery, i believe the heater comes from it
b) what happens if it gets cold, some lifepo4 batteries dont like the cold

MG4 related but same architecture as ZSEV afaik??

(As far as I know)

Maximum Load from 12V Battery
The DCDC Converter LV Side Current is listed at 32A in real-time operation.

The DCDC Converter LV Side Voltage operates at 12V-16V, typically 14.1V.

This suggests that the maximum continuous power drawn from the 12V battery could be around 450W (assuming 14V 32A)

BMS Current Rating.
The high-voltage battery current can vary between -400A to 800A depending on operation.

The BMS relay cutoff occurs if the bus current exceeds 10A for more than 5 seconds during power-down.

The MG4's heater draws its power from the high-voltage battery pack. The system includes a high-voltage Positive Temperature Coefficient (PTC) electric heater, which is controlled by the A/C controller.

The high-voltage power distribution unit (PDU) transmits electricity from the battery pack to the electric heater, electric A/C compressor, and high-voltage battery pack heater.

On models equipped with a heat pump system, the vehicle prioritizes heat pump heating to reduce power loss from the main battery and increase driving range. The electric heater is used as an auxiliary heating source when necessary.

HTH.

 

[ZiggyStandard]

really insteresting thanks, i have 2 questions,
a) what is the current rating needed for the BMS or the maximum load the MG takes from the 12V battery, i believe the heater comes from it
b) what happens if it gets cold, some lifepo4 batteries dont like the cold

I'm still investigating the cold performance of the battery, but it hasn't stopped it working yet. I plan to add some heating pads and insulation.

 

[Coulomb]

Maximum Load from 12V Battery
The DCDC Converter LV Side Current is listed at 32A in real-time operation.

Err, the 2022 ZS EV DC-DC is rated at 178A. But I don't believe that you would ever see that sort of current from the 12V battery.

32A sounds reasonable, though current draw can add up fast under some conditions. Imagine a freezing cold night with the HVAC blower up high, lights on, wipers, and your knee accidentally presses the start button. The 12V battery has to power all that, plus brake lights, computers, pumps, and pull in the HV contactors to get back to ready mode.

There may also be a legal requirement, e.g. the ability to run the hazard lights for 25 minutes. That might be an Australian requirement that is stuck in the back of my head (NCOP-14 from years ago). But it sounds like a reasonable capability to aim for.