I recently bought a 12v deep cycle battery 75 AH and I made a battery box following these tutorials: https://www.youtube.com/watch?v=cAErwLnsSIY and https://www.youtube.com/watch?v=torSEtjPZ2I (no need to watch it ofc, just to understand the basic idea).

A small description how it wires as well: The battery is wired to the first fuse in the fuse block, which is wired to the "master switch", this switch gives power to the rest of the fuses which are wired to other components, and also gives power to the voltmeter for measurement of course.

The problem is that whenever I'm using other components such as leds etc the voltage in the voltmeter is dropping(not the actual battery voltage, but the voltage the voltmeter is reading) and I'm not sure how to change that.

for example, when turning the master switch, the voltmeter is reading 12.5v, then I'm turning on the leds and the voltage is dropping to 12.4v in the voltmeter and so on.

I can wire the voltmeter directly to the battery, but I don't want it to be powered all the time. I'm not 100% sure how it works, but I tried wiring the switch to the voltmeter, and from the voltmeter to the fuse block, but it still doesn't work. Any ideas?

Here are some pictures of the battery box, not great quality, and the wires are currently very messy until I'll fix everything: https://i.sstatic.net/mZaNe.jpg

Thanks, hope I made myself clear enough.

  • \$\begingroup\$ Anyone else maybe? :) \$\endgroup\$
    – argondsd
    Nov 2, 2018 at 10:46

1 Answer 1


The battery has some internal resistance, so when you draw current from it, the output voltage will drop - how much drop will depend on the load current.

The small wires you appear to be using may also have significant resistance, and again will cause some voltage drop. Likewise, there will be a small voltage drop across the fuses.

I wouldn't be surprised by a few tenth's of a volt drop with some load.

  • \$\begingroup\$ Thanks for the answer, but let me clarify it a bit, first I'm using 16 gauge wires, I don't know if its good enough, but I think it should be at least decent, it is possible that there is some resistance in the cables/fuses/somewhere else, but the real problem is that if I power something, the voltage drops from like 12.5v to 12.2v when powering a few components, on the other hand, if I'll connect the voltmeter to the battery directly, it won't drop as much and will display the actual voltage. Voltage drop is understandable, but I'm looking for a wiring solution here :) Thanks! \$\endgroup\$
    – argondsd
    Nov 2, 2018 at 0:00

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