Main battery switching, a different approach

**Snackchaser** · 2026-06-04T01:02:31Z

There are many great postings for installing a main battery switch. Folks like them for safety reasons, to kill parasite loads during storage, or for when working on the system. But I’m not a big fan because the safety benefits are more mythical than real, and 96% of parasite loads can be killed by shutting off the 60 amp DC panel breaker. I just don’t like introducing unnecessary resistance in the high current battery circuit. In rare cases when the main battery circuit needs to worked on, the battery can be disconnected, or the 300 amp breaker can be opened.

Even with liability exposure, Oliver’s decision not to have a main battery switch was a deliberate and sound engineering choice in my opinion There may be some merit-worthy arguments for one, or perhaps a lingering perception that one is needed because it’s a requirement in the marine industry for different risks. In reality, the need to cut power in 12-volt RV systems during emergencies is rare and not normal practice. Besides, most firefighters are trained to cut battery cables before looking for a switch, or trusting it. There is no shock hazard from the battery, and breakers and fuses are more reliable protection against fire hazards, than relying on the right person being in the right place at the right time to find a switch.

I've seen a number of battery switch installations that completely disconnect the battery. This can actually create more credible safety hazards than it prevents. A towed trailer with its battery switched off has no emergency breakaway brakes and no gas or CO detection, both of which should never be switched off. The solar and AC chargers are also disabled in that configuration.

However, switching off parasite loads is definitely a good idea for storage, but it doesn’t require switching off the entire battery.

In the example shown below, the DC panel carries 96% of the parasite load. The remaining 4% of parasitic load comes from the inverter/charger, solar charger, and LP/CO alarm which are all connected directly to the battery. I don't believe it's necessary or advisable to disconnect these circuits for normal off-season storage because those parasite loads are non-consequential. For unusually long storage periods, some additional battery maintenance would be needed regardless.

The parasite load percentages below are based on precise measurements of my Oliver trailer with a 390 amp battery, your setup and amperage may vary. They include electronic standby currents from various LEDs, memories, displays, power supplies, and such. There is no singular large load, but they collectively add up:

Circuit	Draw
DC Panel load	0.48 A	96%
Inverter, Solar Charger, Gas/CO detector	0.02 A	4%
Total measured from battery	0.50 A	100%

DC panel breakdown:

Fuse	Circuit	Draw
2	Various electronics	0.117 A
4	Furnace	0.012 A
5	Main lighting	0.003 A
6	Fans	0.016 A
7	Truma water heater	0.113 A
8	*Furrion Radio	0.204 A
9	USB outlets	0.007 A
10	USB outlets	0.009 A
	Total	0.481 A

*My new IRV stereo is only 0.083 A

Under ideal conditions, a 0.481-amp load from the DC panel would deplete a 390 amp-hour battery in roughly 34 days. Real-world depletion will be faster due to BMS overhead and temperature effects. The remaining 0.02-amp load from the non-DC Panel circuits would take approximately 2.2 years to deplete the battery. A lead acid battery system without inverter would have less parasite draw with the DC panel shut off. It would still last a 7 month storage season before depleting the batteries to a safe 50% discharge.

I used to turn off the DC panel with its 60 amp breaker under the street-side bed. Although effective, it’s inconvenient to reach. This modification provides a more convenient way to turn it off with a latching solenoid relay controlled by a small switch. Latching means it holds position without any power draw, it only consumes current for the instant it switches, adding nothing to the parasite load. These relays are designed for exactly this purpose and are commonly used in boats and RVs. I used an Intellitech style RV latching relay rated for 100 amps.

The relay mounts next to the 60-amp breaker. The existing DC panel feed wire is moved from the breaker output — to the relay output. A new #4 AWG jumper goes from the vacated breaker output — to the latching relay input. Premade made jumpers with ring terminals are readily available in 6” & 12” lengths.

Note: The 60 amp breaker may also have other loads such as the electric jacks. The jacks do not have parasite loads, but turning them off is a form of anti-theft protection to prevent the trailer from being towed away with jacks deployed. If you choose to move these loads to the relay, then the ring terminals need to be enlarged from 1/4” to 5/16” stud size to fit the relay.

Use a sheet metal step drill to enlarge the terminal ring lugs while holding them with pliers, otherwise a twist drill will grab and destroy it. Step drills are great for drilling chip free holes in fiberglass tool.

The relay is controlled with a Double Pole Double Throw (DPDT) momentary switch with a spring return to center. This is the same type of polarity-swapping switch used for the electric jacks. The switch can be located in any accessible and convenient location. I put mine in the battery compartment and wired it with a jacketed 4-conductor 18-gauge cable. The cable fits snugly through a 5/16” hole drilled next to where the DC panel wire penetrates the battery compartment.

I linked one option for a switch mounting bracket. However, I made my own 3-D printed bracket with a red label to identify it as the DC panel shutoff. The print STL file is available, or I have a few extras if anyone needs one. I mounted the switch bracket with high strength double-stick foam tape and stick-on zip-tie mounts for the wire.

The DC panel can now be turned on/off with the switch, without disturbing the inverter/charger, solar charger, or safety circuits. Newer Olivers have a solar disconnect switch and it’s possible to use the latching relay to disconnect the solar too. However, there is limited space on the relay’s stud for circuits so a terminal block would be needed for that purpose.

I couldn’t find decent wiring instructions for the relay, so I provided a sketch. The relay comes with two fuses, use the one connected to the V+ input to power the switch. The other fuse is for an optional switch indicator LED. The switch’s V+ wire connects directly to the fuse spade with a female spade terminal.

BTW: As seen in the picture, my installation is way more congested than normal due to other modifications. I have a large piece of plywood for mounting all my gadgets, you may need to glue a small wood mounting block for the relay. Just trim the insulation and use a good construction glue or epoxy.