max. amount of Lithium batt. in parallel

[Hermia II]

Let me tag along with T1 Terry above who seems very initiated. What I have managed to learn from my Victron installation which comprises 8 batteries 12v 200Ah -> 24v 800Ah in this system where the BMS communicates with the batteries through a separate data bus is:
* The BMS communicates with each cell. You can also check each cell your self with Victron Connect BlueTooth interface.
* I think I have seen a balancing between the cells in one battery, the Victron connect shows 14,xx volt and the there can be a difference in the 1/100 volt figure that evens out. So far all cells have been the same 1/10 of a volt and only ±0,02.
* It can identify a single cell and having parallel batteries prevents damage of the alternator if one battery is cut off.
* Overload is handled by the BatteryProtect controlled by the BMS
* Maximum charge and discharge in terms of capacity (voltage) is handled by the BMS which controls the shore power charger and has functions for cutting an alternator.

But then we are moving on, because the alternator is the next problem. It will fail if you cut the batteries, and it will broil if you don't limit the output so it is a good idea to use lead batteries as starter batteries and LiFePo4 as service, and charge both using a Mastervolt Charge Mate Pro to limit the output to the LiFe batteries. This way you can cut the LiFe without damaging the alternator. The alternator needs to be able to handle 40A continuously, maybe from a 75A alternator. I tried using my 24v/75A charging the 24v/800Ah bank. It delivered 60A at 26,7v (the limit is 28,4v) and after 1hr the temp of the Mastervolt alternator body was 270°F (130°C) which is way too high. I thought it was o'kay since the rated capacity was 75A but despite good ventilation 60A continuously was too much.
As for ShorePower you will at least need a specifically programmed charger for the LiFePo4. Preferably a Victron Multiplus (if you use a Victron Ve-Bus BMS) otherwise you have to be very careful not overcharging the batteries. Max voltage is 14,2v or 28,4 which is less than for the lead cells, but I think you can use this for both since you will also top up the starter batteries with the alternator when running the engine. You can not use a lead cell charger for the LiFe batteries.
Please do not think this is simple, it will involve your complete charging infrastructure.

[goboatingnow]

The last two lines are the key

[T1 Terry]

Originally Posted by Hermia II

Let me tag along with T1 Terry above who seems very initiated. What I have managed to learn from my Victron installation which comprises 8 batteries 12v 200Ah -> 24v 800Ah in this system where the BMS communicates with the batteries through a separate data bus is:
* The BMS communicates with each cell. You can also check each cell your self with Victron Connect BlueTooth interface.
* I think I have seen a balancing between the cells in one battery, the Victron connect shows 14,xx volt and the there can be a difference in the 1/100 volt figure that evens out. So far all cells have been the same 1/10 of a volt and only ±0,02.
* It can identify a single cell and having parallel batteries prevents damage of the alternator if one battery is cut off.
* Overload is handled by the BatteryProtect controlled by the BMS
* Maximum charge and discharge in terms of capacity (voltage) is handled by the BMS which controls the shore power charger and has functions for cutting an alternator.

But then we are moving on, because the alternator is the next problem. It will fail if you cut the batteries, and it will broil if you don't limit the output so it is a good idea to use lead batteries as starter batteries and LiFePo4 as service, and charge both using a Mastervolt Charge Mate Pro to limit the output to the LiFe batteries. This way you can cut the LiFe without damaging the alternator. The alternator needs to be able to handle 40A continuously, maybe from a 75A alternator. I tried using my 24v/75A charging the 24v/800Ah bank. It delivered 60A at 26,7v (the limit is 28,4v) and after 1hr the temp of the Mastervolt alternator body was 270°F (130°C) which is way too high. I thought it was o'kay since the rated capacity was 75A but despite good ventilation 60A continuously was too much.
As for ShorePower you will at least need a specifically programmed charger for the LiFePo4. Preferably a Victron Multiplus (if you use a Victron Ve-Bus BMS) otherwise you have to be very careful not overcharging the batteries. Max voltage is 14,2v or 28,4 which is less than for the lead cells, but I think you can use this for both since you will also top up the starter batteries with the alternator when running the engine. You can not use a lead cell charger for the LiFe batteries.
Please do not think this is simple, it will involve your complete charging infrastructure.

Victron do make very good DC to DC chargers that can be controlled by a BMS and displayed on a Bluetooth capable phone. When using the Victron products, be sure to use all "Smart" identified units because they have the ability to network with each other and this eliminates the multiple chargers on a single battery issue that was common in just about all MPPT charging devices. This means if you have an alternator that can handle continuous high output, multiple Victron DC to DC devices can be used to charge the one lithium battery and the end of charge voltage can be staggered so the final charging is controlled by a single unit and a gradual tapering off occurs rather than a snap on/off that does influence cell voltages when close to 100% SOC and can cause big voltage fluctuation on the lead acid start battery and anything powered from there.

There are a lot of good BMS systems out there, but as far as I know, Victron is the only system that will work with multiple batteries in parallel .... and you do pay for that ability but get a good product as well.
I use a number of the latest "Smart" Victron products because they work as designed, I don't use their batteries or BMS, purely on a cost basis

T1 Terry