To Fuse or Not to Fuse - New 12v 600 amp hr RV battery

[CaptainUnderpants]

Currently there is a 12V 300 amp hr Relion RB300 battery in my Ford Transit Campervan. The battery positive goes to my Victron Lynx and is currently protected by a 400 amp Class T fuse. My largest draw is my Victron Multiplus 12v 3000.

I plan on replacing the Relion with a 12v 600 amp hr DIY battery. The battery will consist of 2 x 12v 300 amp hr batteries each with a 4s Overkill BMS 120amp (discharge or charge) 8 cells total.

My question is: should I add any additional Fuses or Circuit breakers or should the Overkill BMS's provide enough fault protection?

Something like:
[4s Overkill BMS] - 150a Circuit Breaker \
Parallel Connected ................................................Bus Bar - 400amp Classt T - Victron Lynx
[4s Overkill BMS] - 150a Circuit Breaker /

My gut feel is that this extra protection is theoretically good, but practically not needed. If this extra protection IS needed, should I be using Mega Fuses or another Class T fuse instead of a circuit breaker?

 

[JoeHam]

Currently there is a 12V 300 amp hr Relion RB300 battery in my Ford Transit Campervan. The battery positive goes to my Victron Lynx and is currently protected by a 400 amp Class T fuse. My largest draw is my Victron Multiplus 12v 3000.

I plan on replacing the Relion with a 12v 600 amp hr DIY battery. The battery will consist of 2 x 12v 300 amp hr batteries each with a 4s Overkill BMS 120amp (discharge or charge) 8 cells total.

My question is: should I add any additional Fuses or Circuit breakers or should the Overkill BMS's provide enough fault protection?

Something like:
[4s Overkill BMS] - 150a Circuit Breaker \
Parallel Connected ................................................Bus Bar - 400amp Classt T - Victron Lynx
[4s Overkill BMS] - 150a Circuit Breaker /

My gut feel is that this extra protection is theoretically good, but practically not needed. If this extra protection IS needed, should I be using Mega Fuses or another Class T fuse instead of a circuit breaker?

Your BMS is NOT an adequate substitute for an OCPD (over current protection device).

The FETs in BMS’s can, and sometimes do, fail closed. Not a theoretical thing.

Each battery needs an OCPD as close to the battery as practical.

I would use a properly rated DC breaker or a class T fuse.