12V Battery: FLA or AGM?

[stevedee]

My special thanks to @Joningy for pointing out that his 12V battery, is in fact an FLA.

And apologies to everyone for my naivety; I had assumed that in 2025, all ev manufacturers had stopped using FLA and were either using AGM or lithium technology. I was nearly right, but MG have stuck with the cheaper option.

I only had to lift the bonnet of the car and slide the battery strap to reveal that my S5 also has an FLA...

​

This is very disappointing.

Since the S5 12V battery control system is 'tuned' for the requirements of a flooded battery, fitting an AGM would probably be a bad idea.

Attached is the opinion from chatGPT.

 

[Lovemyev]

My special thanks to @Joningy for pointing out that his 12V battery, is in fact an FLA.

And apologies to everyone for my naivety; I had assumed that in 2025, all ev manufacturers had stopped using FLA and were either using AGM or lithium technology. I was nearly right, but MG have stuck with the cheaper option.

I only had to lift the bonnet of the car and slide the battery strap to reveal that my S5 also has an FLA...


View attachment 42928

​

This is very disappointing.

Since the S5 12V battery control system is 'tuned' for the requirements of a flooded battery, fitting an AGM would probably be a bad idea.

Attached is the opinion from chatGPT.

That is a very detailed and comprehensive explanation of the rights and wrongs for fitting a new battery to the S5.
Other MG models as well, by the looks of it.
So, basic flooded battery it is then !.
The recommendation of increasing the size / capacity is the only viable option.
Which would be a sensible idea I think.
Together with improving the quality of the unit that would include a 5 year warranty.
4 more years than the factory fit unit of course !.

 

[T1 Terry]

My special thanks to @Joningy for pointing out that his 12V battery, is in fact an FLA.

And apologies to everyone for my naivety; I had assumed that in 2025, all ev manufacturers had stopped using FLA and were either using AGM or lithium technology. I was nearly right, but MG have stuck with the cheaper option.

I only had to lift the bonnet of the car and slide the battery strap to reveal that my S5 also has an FLA...


View attachment 42928

​

This is very disappointing.

Since the S5 12V battery control system is 'tuned' for the requirements of a flooded battery, fitting an AGM would probably be a bad idea.

Attached is the opinion from chatGPT.

Can you look further on the label and see what it says regarding CCA and RC values ..... and if it does actually have an Ah rating or is the B35F leading members to thinking it is a 35Ah battery, where it is just a model identifier.

A properly constructed LFP, lithium titanate and sodium ion battery will work best with such a poor charging regime, that 14v won't be reached until the battery is nearly fully charged, none of these type of battery suffer any ill effects from not being fully charged each time or being fully charged, as long as there is a cell equaliser in the build that can transfer a decent number of amps, 5 amps or more is good, 0.05 amps or 5 milliamps is a complete joke for anything bigger than a AA battery.

T1 Terry

 

[stevedee]

Can you look further on the label and see what it says regarding CCA and RC values .....

Sorry I should have previously posted this...

 

[T1 Terry]

Sorry I should have previously posted this...

View attachment 42931

If it really is a 35ah flooded cell deep cycle battery, which I doubt, they are expensive, the charging profile that has been mentioned will not recharge the battery. It would need to remain at the 14v for 12 hrs to fully recharge it.
The small white plastic plug shown at the end of the top casing suggests that is where the vent tube is supposed to go and this is an example of a late design cold cranking battery, it even has the 280A in the CCA column, which is nonsense, it wouldn't supply 25 amps constant for 280 minutes, 4.6 hrs ....

T1 Terry