Stranded, Stop Safely Now, 12volt battery dies

shelnian

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Lead acid batteries do not like to be drained all the way, and in fact may not recharge if totally discharged. Lead acid batteries don't like to be discharged more than 50% of their rated amp hours on a regular basis. I don't know why Ford would use a cheap lead acid 12v battery when there are many Li-ion and LiFePO4 batteries that have built in battery management circuits that turns the battery OFF when it gets to low, so it doesn't fail. These batteries also allow about 80% of the rated amp hours to be used on a regular basis like the MME main battery pack. Wonder if the 12v lead acid battery can be replaced with a LiFePO4 battery. The charger specs would be needed.

 

dtbaker61

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Lead acid batteries do not like to be drained all the way, and in fact may not recharge if totally discharged. Lead acid batteries don't like to be discharged more than 50% of their rated amp hours on a regular basis. I don't know why Ford would use a cheap lead acid 12v battery when there are many Li-ion and LiFePO4 batteries that have built in battery management circuits that turns the battery OFF when it gets to low, so it doesn't fail. These batteries also allow about 80% of the rated amp hours to be used on a regular basis like the MME main battery pack. Wonder if the 12v lead acid battery can be replaced with a LiFePO4 battery. The charger specs would be needed.

there are lots of reasons I'd guess Ford went with AGM for the LVB rather than lithium....
- the Funk is not heated, and Li batteries should not be charged below 0C... which means the LVB would need it's very own BMS and environmental temp control system.... costing more and introducing many more points of possible failure.
- Lead batts fail gradually, predictably, and you can tell exactly what SOC is without a BMS counting ah
- over-discharge of lead batts may reduce cycle life, but they almost always recover enough to run long enough to replace.

the point is that the little AGM *should* be fine if sensors are working correctly, and it 'wakes up' the HV->dc-dc system to obtain a charge when needed (when it drops to 12.0).
 

shelnian

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there are lots of reasons I'd guess Ford went with AGM for the LVB rather than lithium....
- the Funk is not heated, and Li batteries should not be charged below 0C... which means the LVB would need it's very own BMS and environmental temp control system.... costing more and introducing many more points of possible failure.
- Lead batts fail gradually, predictably, and you can tell exactly what SOC is without a BMS counting ah
- over-discharge of lead batts may reduce cycle life, but they almost always recover enough to run long enough to replace.

the point is that the little AGM *should* be fine if sensors are working correctly, and it 'wakes up' the HV->dc-dc system to obtain a charge when needed (when it drops to 12.0).
https://battlebornbatteries.com/lead-is-dead-white-paper-study/
Why install a battery that will need to be replaced in 3 to 5 years when they could have installed one that lasts longer than the main battery?
 

dtbaker61

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https://battlebornbatteries.com/lead-is-dead-white-paper-study/
Why install a battery that will need to be replaced in 3 to 5 years when they could have installed one that lasts longer than the main battery?

did you not read my response?

most 12v Li batteries do not have internal heaters... BattleBorn included. The whitepaper you reference says " If the battery is in a cooler environment, the BMS will trigger and keep the battery from taking a charge as long as the temperature is below 32° F. "

Inability to charge would indeed protect the 12v battery, but it would brick your MME as soon as it discharged and disallowed the HV to re-charge it if the frunk was < 32F.

The AGM battery choice is because huge capacity is not needed, big 'cranking' amps are not needed, and it will hardly be used as long as it gets charged from the HV anytime your MME is 'on'.... at half the cost of Li. The life of the little AGM may be 'who knows' since under normal regular use, the 12v battery should hardly be discharged while sleeping, and then gets fully charged while driving.

 

 
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