Battery cuttoff placement

[jpcjtrtj]

Two questions: I have a 280 AH LIPO4 12V system with no inverter; solar comes in on 2-100 watt panels; I also have a 40 Amp DC DC charger to charge from the car and 55 amp Converter to charge from shore power.

Question 1. Is a manual Battery cut off switch a necessity or convenience. I already have an electronic cutoff, but I assume that is prone to failure? In the prior incarnation of this trailer, the way to disconnect the batteries was to remove the negative wire. That seems just as easy now with the new set up as it was with the old one. . . . so I'm not seeing a compelling reason to add this switch . . . even though I have one. Thoughts? Does the answer change if i add a 200 watt inverter?

Question 2. Explorist and Will and many of the builds on here both show the battery cutoff on the positive terminal of the battery. Everything I've ever read says disconnect the negative terminal first and most things I've read suggest putting the cutoff on the negative side. Which one is right?

 

[Just An RVer]

You need a safe way to isolate your batteries from the rest of your system in a way that doesn't let you accidentally short the lead to something else. With the current-passing capabilities of lithium batteries, a switch seems a heck of a lot less room for error than waggling one of the leads around. There will be some inrush current to the capacitors in an inverter as you connect to the batteries, but if it really is only a 200 watt inverter, there shouldn't be much, if any, arcing. Don't try that with an inverter larger than 2,000 watts, though. That could create an arc and destroy a lug, terminal, or worse.

I will tell you from experience, the easier you make it to disconnect the batteries, the more likely you are to do it every time.

I don't think there's a practical difference whether you switch the positive or negative side. I suspect it's just convention.