Upgrade 12v battery

[ChilledMatt]

The 12v battery seems to be the Achilles heal in many EVs as they are smaller than those typically found in ICE vehicles. Is it possible/economical to replace the 12v battery with a higher capacity offering? Has anyone here done this.
Thanks in advance.

 

[dsimpkins]

There's a thread on the MG ZS forum where someone has just replaced the 12v battery on theirs for a LiFePO4 battery equivilent

 

[TheHypnoToad]

I've not had any issues with mine as the HV battery should charge the 12v battery when it gets low, so I don't see any reason to add any more weight to the car.

 

[tsedge]

The 12v battery seems to be the Achilles heal in many EVs as they are smaller than those typically found in ICE vehicles.

No, this is not the reason. EVs don't need big 12V batteries that can crank over a large engine, because they never have to do this. NB: Never, never jump start an ICE with your EV, you may damage the EV.

They are an achilles heel because:

• 12V batteries are designed for low normal electrical load with occasional massive cranking load: ie for ICE applications.
• EVs never need the cranking load but they can draw a fair bit especially in winter driving all the car's electronics, lighting and other systems directly off the battery.
• A 16V Lithium Ion battery is a better choice for an EV but manufacturers try to cut costs and use a traditional 12V.
• 12V battery quality has massively declined. The race to the bottom has led to low quality batteries that don't last.
• Many EVs have had bugs resulting in inadequate charging of the 12V battery from the main battery.

 

[paulm]

I saw the thread on the ZS but can’t find it just now.

Take care with 12v lithium batteries (LiFePo4) if you charge them below 0c (freezing) you will destroy them (caveat the internal bms may have low temperature protection and there may even be an internal heater on the more expensive quality brands) do your research carefully and diligently before changing.

Paul
P.s. I’m intrigued as to the advantages of a 16v system?

 

[dsimpkins]

No, this is not the reason. EVs don't need big 12V batteries that can crank over a large engine, because they never have to do this. NB: Never, never jump start an ICE with your EV, you may damage the EV.

They are an achilles heel because:

• 12V batteries are designed for low normal electrical load with occasional massive cranking load: ie for ICE applications.
• EVs never need the cranking load but they can draw a fair bit especially in winter driving all the car's electronics, lighting and other systems directly off the battery.
• A 16V Lithium Ion battery is a better choice for an EV but manufacturers try to cut costs and use a traditional 12V.
• 12V battery quality has massively declined. The race to the bottom has led to low quality batteries that don't last.
• Many EVs have had bugs resulting in inadequate charging of the 12V battery from the main battery.

In that case, would a 12v deep cycle (leisure type) battery be a better choice in an EV because it is designed to handle drawing a fair bit of current for a longer period?

 

[tsedge]

I saw the thread on the ZS but can’t find it just now.

Take care with 12v lithium batteries (LiFePo4) if you charge them below 0c (freezing) you will destroy them (caveat the internal bms may have low temperature protection and there may even be an internal heater on the more expensive quality brands) do your research carefully and diligently before changing.

Paul
P.s. I’m intrigued as to the advantages of a 16v system?

Lithium batteries run below the rated voltage, so 16V is the equivalent of a 12V traditional battery, some of them are labelled 16V, some as 12V equivalent.

Those intended for car use can cope with the low temperatures no problem.

 

[tsedge]

In that case, would a 12v deep cycle (leisure type) battery be a better choice in an EV because it is designed to handle drawing a fair bit of current for a longer period?

Yes, absolutely, but they are very expensive by comparison to the el cheapo ones they fit by default.

 

[paulm]

Lithium batteries run below the rated voltage, so 16V is the equivalent of a 12V traditional battery, some of them are labelled 16V, some as 12V equivalent.

If you fit a 16v battery you will need to modify the charger to charge at the correct voltage for the battery and I’m certain that you would invalidate the mg warranty on all the 12v electronics.

 

[tsedge]

If you fit a 16v battery you will need to modify the charger to charge at the correct voltage for the battery and I’m certain that you would invalidate the mg warranty on all the 12v electronics.

I'm not suggesting any DIY change - making the point that some manufacturers have gone the lithium route because of the weaknesses of traditional 12V battery tech.

 

[paulm]

I would go for a quality agm deep cycle battery. I’ve used Odyssey in the past and had over 15 years life but they are expensive.

 

[Kithmo]

Not checked my 4's capacity yet but I know the ZS EV had a fairly large capacity battery, 54Ah IIRC.

 

[johnb80]

Lithium batteries run below the rated voltage, so 16V is the equivalent of a 12V traditional battery, some of them are labelled 16V, some as 12V equivalent.

LifeP04 has a terminal voltage of 3.7v, 4 cells in series would give 14.8v which is slightly above the normal 12cv systems in a car, generally 13.8 or 14.4 when charging. 14.4 charging voltage wont be enough to fully charge the LifeP04 but it will get fairly close.

Those intended for car use can cope with the low temperatures no problem.

The low temperature issue for charging is chemistry related, any LifeP04 based battery that can operate below zero when charging must have a heater built in which does of course consume some of the capacity. I havent found any LifeP04 car batteries online that allow charging below 0 degC which may be a major issue with some cars systems, theyre expecting the 12v battery to take charging current but the BMS says no effectively presenting an open circuit to the charging system which may or may not trigger fault codes. Discharging is OK down to -20 deg C or thereabouts. My DIY home battery I have put heater mats under them to prevent low temperatures in winter, I have set their minimum to 5 degC for this reason.

This is an eco-worthy battery, £150

This one is a top of the range Renogy battery at £459

 

[tsedge]

 

[paulm]

Useful for tesla owners but irrelevant for mg owners.

 

[tsedge]

Useful for tesla owners but irrelevant for mg owners.

sigh.... I was responding to John with some info that is clearly on topic. I did not recommend it as an MG replacement!

If I am recommending something as an MG replacement I'll say so, in the meantime please stop qualifying all my posts.

 

[johnb80]

Interesting.........

I'm not confident that Lead Acid can be replaced with a straight forward drop in replacement LifeP04 battery from both a temperature and voltage perspective. I did chew over fitting a LifeP04 battery to my i3 but ruled it out for these reasons.

 

[paulm]

. I was responding to John with some info that is clearly on topic. I did not recommend it as an MG replacement!

If I am recommending something as an MG replacement I'll say so, in the meantime please stop qualifying all my posts.

The originator of this thread was asking specifically about the MG4 12v battery. I know it is interesting to broaden the scope but this doesn’t really help ChilledMatt. Maybe the extended discussion should be moved from the MG4 specific forum to the general ev discussion?

 

[tsedge]

The originator of this thread was asking specifically about the MG4 12v battery. I know it is interesting to broaden the scope but this doesn’t really help ChilledMatt. Maybe the extended discussion should be moved from the MG4 specific forum to the general ev discussion?

Threads are not solely for the originator - they are for the community to engage with and will evolve and develop naturally.

That said, I have no objection if this part of the discussion is moved.

 

[paulm]

I assume Tesla went for li-Ion instead of LiFePo4 for cost and weight reasons. Getting a decent 12 v lead acid equivalent with Li-Ion is more difficult due to the voltage of the cells. Li-Ion and LiFePo4 while both lithium are very different technologies. LiFPo4 is much better suited for a drop in (lead acid) replacement but still requires care depending on the application.