The short answer. Put the battery switch on the house positive, right after the main fuse. Size it by the cable you’ll actually run, not the biggest number on the box. Egis rates its XD switch at 500A continuous only with two 4/0 cables, 300A on one 4/0 and 225A on 2/0. Turn loads and chargers off before you flip it. Victron’s lithium manual recommends switching off when the system isn’t in use.
You’ll need
- A heavy-duty on/off battery switch. Our Boat lithium upgrade kit uses the Egis XD 500A (part 8710-1900)
- A main fuse at the battery, ahead of the switch. See Fusing a lithium bank: Lynx, MRBF and class T
- Cable sized for your current and run length: use the Wire gauge calculator
- A Victron Busbar 250A 4-point with cover for the positive side after the switch
- Tinned lugs to suit each stud, such as the Pacer tinned lug 2/0, 3/8 in stud, 10-pack where the stud is 3/8 inch
- A torque wrench that reads in inch-pounds
Swapping to lithium is a good time to redo the switch. It’s one part, it’s simple, and you’ll know it’s right because you did it. Here’s how.
Where does the battery switch go?
On the positive cable, after the main fuse. The order runs battery positive, main fuse, switch, then the positive busbar that feeds everything else. With the fuse first, it protects the cable to the switch as well as everything after it. The Boat lithium battery wiring diagram: 2 simple setups shows that full chain, negatives and shunt included.
Mount the switch where you can reach it fast, and keep the cable from the fuse short.
Why does the switch rating depend on cable size?
Look at how Egis rates the XD. It doesn’t give one continuous number. It gives three, one per cable setup:
| Cable on the switch | Egis XD continuous rating |
|---|---|
| Two 4/0 cables | 500A |
| One 4/0 cable | 300A |
| One 2/0 cable | 225A |
From the Egis XD Series brochure for part 8710-1900.
So “500A” on the box is only true with two 4/0 cables on each side. A house bank on a single 2/0 run gets 225A from the same switch. Read the line for the cable you’re really using, then check that it covers your biggest steady load (on most boats that’s the inverter).
The other Egis XD numbers worth knowing:
- Voltage: Egis’s brochure and its product page list different voltage ranges, so check the range on the switch’s own label for a 24V or 48V bank.
- Switching under power: rated for live switching at 12V/300A.
- Sealing: IP67.
- Ignition protected: to SAE J1171, per Egis.
- Stud torque: 140 in-lb.
Can you switch a lithium battery off under load?
Here’s what we found in the maker documents, and what we didn’t.
Egis gives the XD a live switching rating of 12V/300A. That’s the switch’s own limit for breaking current.
Victron’s lithium battery manual doesn’t say anything either way about opening a switch with loads running. What it does say is to use the switch. It calls a BMS low-voltage shutdown a last resort, and recommends a battery switch, pulling the battery fuses, or disconnecting the battery positive when the system isn’t in use. Charge the battery enough first, so there’s reserve left while it sits.
The reason is in the same manual. After a low-cell shutdown, about 1 Ah per 100 Ah is left in the battery. Victron’s example: a 10 mA leftover draw can damage a 200 Ah battery that sits discharged for more than 8 days. On a boat, that draw can be a bilge alarm, a radio memory or a charger’s back-drain. A switch that’s actually off stops it.
Our advice: turn loads and chargers off first, then the switch. It’s easy on the contacts, and nothing gets cut off halfway.
One bank, or house plus start?
One bank. If the lithium bank runs everything, including the engine start (check your battery maker’s manual for engine starting), one on/off switch after the main fuse is the whole job.
House plus start. Most boats moving to lithium keep a lead-acid battery on the engine. Our advice is one on/off switch per battery, with nothing that joins the two banks. Engine charge reaches the lithium bank through a DC-DC charger instead. The Boat lithium battery wiring diagram: 2 simple setups shows the second setup with its fuses.
Switch, BMS and BatteryProtect: who does what
Victron’s lithium manual describes two ways a BMS controls the system. Either it tells a load or charger to switch on or off by signal, or it physically connects and disconnects them through a BatteryProtect or Cyrix Li-ion relay.
A Victron Smart BatteryProtect 100A is the physical kind, for a group of loads. Victron rates it at 100A continuous and 600A peak, for 6-35 V systems, with M8 connections. It uses MOSFET switches, not relays, so Victron says there are no sparks. Three rules from its manual:
- Current flows one way, IN to OUT. Reverse current damages it. One unit handles a load or a charger, never both.
- Never put an inverter’s DC input through it. Use the inverter’s remote port instead, with the BatteryProtect switching that.
- Fuse the cable between the battery and the BatteryProtect.
So the jobs split up neatly. The main switch is your hand on the whole system. The BatteryProtect is the automatic cut for loads. The BMS decides when.
How to fit the battery switch: step by step
- Everything off. Loads, chargers, inverter, shore power. Disconnect the battery negative first.
- Size the cable with the Wire gauge calculator, then check that the switch’s rating for that cable size covers the load.
- Fit the main fuse at the battery. Size it to the cable. See Fusing a lithium bank: Lynx, MRBF and class T.
- Mount the switch on a solid surface, within easy reach and close to the fuse.
- Crimp tinned lugs with a hole that matches each stud. Seal them with adhesive-lined heat shrink.
- Connect fuse to switch, then switch to the positive busbar.
- Torque to the maker’s numbers. Egis lists 140 in-lb for the XD studs. Victron lists 110 lbf-in (13 N-m) for its 250A busbar, which has 5/16 inch (8 mm) studs.
- Cover every positive stud. Victron’s busbar comes with a cover.
- Reconnect and test. Switch on, check the busbar has voltage, switch off, check it’s gone.
Write the torque numbers on a tag by the switch. Next time you check the lugs, they’re right there.
Does this guide fit your boat?
This applies if: – Your bank is 12V DC. For 24V or 48V, check the switch’s voltage rating on its label (Egis’s brochure and product page disagree). – You’re moving to lithium, or rewiring around one. – Your steady load sits inside the switch’s rating for your cable size.
This doesn’t apply if: – You’re working on the AC side or shore power. That’s a job for a licensed electrician. – Your lithium battery has its own built-in switch or contactor. Follow that maker’s manual first. – Your system is above 60 V.
Products used in this guide
| Product | Why it’s here |
|---|---|
| Victron Busbar 250A 4-point with cover | The positive busbar after the switch. 250A max, 70 VDC max, 5/16 inch studs. |
| Victron Smart BatteryProtect 100A | Automatic load cut. 100A continuous, IN to OUT only. |
| Pacer tinned lug 2/0, 3/8 in stud, 10-pack | Tinned 2/0 lugs for 3/8 inch studs. Check each stud size first. |
The Egis XD switch comes in the Boat lithium upgrade kit. Fuses, switches and busbars are in Switches, fuses and busbars. Prices show live from the store.
Bundles for this job: Boat lithium upgrade kit, small, Boat lithium upgrade kit, large
Quick answers
Is a 500A battery switch rated 500A on any cable? Not the Egis XD. Egis rates it at 500A continuous only with two 4/0 cables, 300A on one 4/0 and 225A on 2/0.
Does the battery switch go before or after the fuse? After. Main fuse at the battery first, then the switch, then the busbar.
Should I turn off my lithium battery when the boat sits? Yes, once it’s charged enough. Victron’s lithium manual recommends a battery switch, pulling the fuses, or disconnecting the positive when the system isn’t in use.
Can I use a BatteryProtect as my main switch? Not for chargers and loads together, or for an inverter’s DC input. Victron’s manual says it carries current one way only, and an inverter must be controlled through its remote port.
Is the Egis XD ignition protected? Yes. Egis lists it as ignition protected to SAE J1171, and sealed to IP67.
Sources
- Egis maker PDF (XD Series brochure, 8710-1900), no public link found Nov 4 2026
- Victron Lithium Smart Battery manual rev 21: https://www.victronenergy.com/upload/documents/Lithium_Battery_Smart/15958-Manual_Lithium_Smart_Battery-pdf-en.pdf
- Victron Smart BatteryProtect 12/24V manual rev 05: https://www.victronenergy.com/upload/documents/Smart_BatteryProtect_12V_24V/114439-Smart_BatteryProtect-pdf-en.pdf
- Victron Busbar 250A 4P and 6P datasheet: https://www.victronenergy.com/upload/documents/Datasheet-Busbar-250-A-4P-and-6P-with-cover-EN.pdf
