question

Its VERY Very unlikey to be the MPPT , as long as it was setup with the correct voltage settings has been done.

There are many reasons/possibilities for this sort of failure

However as the battery's BMS in your case (from what you have said) controls the cells and manages the battery if there was a overvoltage or undercharge then the BMS would disconnect that battery, as thats its job. in a stand alone battery

Personally having 4 multi stand alone batteries that are all having internal BMS with internal shut off in the battery - in a system is not a good way to go, you should be having a intergrated BMS that works with the power systems and advises all systems on when to reduce change or to stop or reduce loads.

using a battery system thats integrated into each battery means that a battery can turn off and you will never know - unless you check them manually on a regular basis.

Your failure is more than likley a battery thats disconnected because of a low cell voltage and stayed disconnected and the cells voltage has continued to drop lower and lower until it swells and smokes, or it was NOT correctly cell balanced from the very start.

If a overcharge did occur then all cells would more than likley be damaged in that battery.

However saying the above really depends on your complete setup and what style of battery's you have,

Hi @solseekerssolar

To be straight up with the potential, it is possible for the Victron MPPTs (excluding RS models which are galvanically isolated) to connect PV voltage directly to battery voltage in the unlikely event of a particular type of fault.

It is rare, but it can happen. It is not a transitory failure, if this fault has occurred the unit would now permanently be in that state.

If you're concerned about the MPPT, please take it to your Victron dealer and ask them to perform a pre-RMA check on it. That procedure will test to see if this is occurring.

The procedure to test is step 6 of the MPPT pre-RMA check and is described here - https://www.victronenergy.com/upload/documents/Pre-RMA_bench_test_instructions/114199-Pre-RMA_bench_test_instructions-pdf-en.pdf

There are 100,000's of Victron 100/50 MPPTs in the field, they are a workhorse model and there is no specific variation in their design, or statistical failure rate compared to the rest of the range. To give the claim the benefit of the doubt, because there are so many of them, anecdotally they might see more of them and presume there is some problem with that model.

@solseekerssolar Further to what has already been written, it might be an idea to review the way the batteries have been paralleled, and fusing requirements.

Recommended ways to parallel 4 batteries from Wiring Unlimited.

It would also be a good idea to fuse each battery on the positive batt post. This will ensure that if one battery has a failure, the other 3 batteries don't gang up and set fire to the battery having a bad day.

Reading the replies reminded me that a friend's had exactly the same problem on his boat. Battery was 4 cells in series, external BMS. BMS faulty, was fixed, failed again, supplier didn't fix. Failed BMS overcharged one cell which failed with short circuit when it swelled up. Other cells then split the charge voltage between them. All wrecked.

Reading this thread again reminded me of something. I used to live in an area with high incidence of lightning strikes. Electric gate failures due to lightning were a regular problem. Didn't even need a direct strike.

A friend made quite a good income fixing the gates and protecting the circuitry with electronics that would safely conduct the spikes to earth. It should be possible to design something to do the same for PV systems. Sadly I've lost contact with my friend, so no way of finding out what he did. But mine never failed. But I guess it's a rare enough occurrence that would not justify the effort of product development..