Sorry for the novel
Let me count the ways you could have issues:
1. Mounting it all in wood - appears to be partical board shelf. Bad idea - buy a metal/wire shelf that is strong enough for you to stand on. More than one post in the "Up in smoke... learn from my mistake!" forum started with partical board shelves. Put the batteries on a lower shelf, cut a piece of Durock cement board like they lay tile with to mount everything else on. Nothing flamable touching any part of it.
2. Using an ANL fuse inline with 4 parallel batteries - should be a class T - lookup AIC
3. With 4 in parallel you should use a pair of bus bars, 600amp rated - 400 plus 20% is 480. Nearest size is 600amp. Make sure they aren't cheap no-name. If you insist on running wires instead of bus bars, put a 125a MRBF fuse and holder on the positive post of all batteries.
4. Those breakers - if they aren't blue sea or eaton or quality they will likely have a firey fail.
5. This is opinion - that sort of hammer crimper is really only intended as an emergency. To do a proper crimp you need a 2lb sledge and anvil or solid surface. It takes a pretty hard hit. If the lug bends in the process the lug is to thin a metal. The right lug is thick walled to use in these.
Get a quality hydraulic crimper (temco or good brand, not the $40 version on amazon or from harbor freight) or order cables to length fron windy nation. This isn't opinion - if you crimp cables and it leaves wings the die size is incorrect or the lugs aren't the right specs. A lot of the cheap ones are marked in AWG and are actually metric. To pass an inspection the wire size must be imprinted in the metal of the crimp.
6. What brand and type of lugs did you use? Many of the cheap ones on amazon are thin crap. Do they have UL and size listings on them? Selterm, temco, Ancor, or marine rated lugs. If you use the cheap crappy ones most of the time they leave wings from not fitting the crimper and wire correctly.
7. I would buy enough rubber boots to cover the ends of every cable. Exposed metal is asking for a short.
8. Did you use any anti-oxide compound on all your connections? If not order a can of No-Ox-ID and put a thin coat on all connections. It keeps corrosion at bay and will cut through any lite oxide coating present on the battery terminals. No-ox-id is conductive dark colored grease. It is not the white stuff in the tube manufactured by Ideal.
9. Every wire in your system should be fused. Either inline or preferably at the point closest to the power source.
10. Try not to stack lugs and terminals. If you must biggest goes closest to the bus bar. And don't stack more than 2 high. Make sure to ONLY use washers. Not saying you are as I can't tell from the pictures.
11. If any part of your system is to warm to touch and hold your hand on, you are doing something wrong.
12. If this is in a living space get a battery powered smoke detector that is the ionizing variety. That will alarm based on smoke if something gets hot. Even if you can't see the smoke. And if there is actually a fire it will alarm as well. The standard type smoke alarm only alarms on smoke breaking an infrared beam inside it, so the smoke has to be pretty thick. The ionizing ones cost about $30 verse $10 but are well worth it.
ideally put this in the garage and run an AC cord into the house through a hole in the wall. Seal around it. Garage walls are generally required to have a 4 hour burn time before the fire can get into the living area.
What kind of cable are you using? There are many kinds and temperature ratings. Pretty much all of your cable should be welding wire 105c rated.
You may think the fuses and nothing flamable is overkill but the math shows - if you short a wrench across one of the batteries - all 400amps will cross through it. A MRBF on the post takes 0.01 to 0.1 seconds to blow. In that time the wrench will hit around 145F in 0.1 seconds and if not corrected the wire insulation melts in around 2 seconds. In around 5 minutes the wrench is red hot and melts. This assume 2/0 welding wire between the batteries. And it assume the BMS limits current to 100a per verse just shutting down. BMS control current by manipulating MOSFETs to turn them off and on, and there is a chance for them to fail shorted until they burn open.
So if you have fuses the most likely outcome is you pop all 4 of them because of how they are wired. If you switch to bus bars you put a MRBF/class T at the bar end and depend on the BMS to shut down current on one battery. Drop that wrench or otherwise cut the wire and you pop 1 fuse.
