Help and FAQ

Pick one rated above everything you’ll run at once. Here’s how:

1. Add up the watts of everything that runs at the same time.
2. Choose an inverter whose continuous rating is above that total.
3. Fridges, pumps and power tools pull extra for a moment when they start, so check the surge rating against the start-up figure on the appliance label.
4. Size the battery cables for the draw: at 12V it’s about the watts divided by 12 in amps, plus a little for losses.

The sizer below does the math. Connecting the inverter’s AC output into a boat or RV panel is a job for a qualified electrician.

Inverter sizer · Wire gauge calculator

Divide the AC watts by the battery voltage. A 1,000W load on a 12V battery is about 83A, and a bit more in practice because the inverter and the cables lose some power as heat. Victron’s own worked example is a 2,400W load at 12V, about 200A before losses. That current is what your battery cables, main fuse and battery monitor have to be sized for.

Inverter sizer · Wire gauge calculator

Victron’s wiring book gives 12V systems a preferred upper limit of 3,000VA. Above that, the battery current gets so high that cables become very thick, so they suggest moving to 24V (up to 5,000VA) or 48V. If you have 12V-only gear on a higher-voltage system, a DC-DC converter can feed it.

Inverter sizer

For boats, vans and RVs, pure sine is the safe pick: it runs electronics, chargers and motors the way shore power does. The inverters we list are pure sine models from Victron and Samlex; each product page shows the full specs.

Work out what you use in a day, then size the bank to cover it. Here’s how:

1. List each thing you run, its watts and its hours a day.
2. Multiply and add them up: that’s your watt-hours per day.
3. Divide by 12 for amp-hours at 12V.
4. Divide by how much of the battery you plan to use (the depth of discharge on your battery’s datasheet, as a fraction).
5. Add extra for days without charging.

Trolling motor? Take the amps it draws at the speed you usually run (it’s on the motor maker’s spec sheet), times your hours on the water. That’s your amp-hours before step 4. Check the motor’s voltage: 12, 24 or 36V means one, two or three identical 12V batteries (same model, size and age) wired in series. Series adds volts, not amp-hours, so your step 4 answer is the size of each battery. Charge with a multi-bank marine charger.

The bank sizer below does it in one go.

Battery bank sizer · Trolling motor batteries

Current and length decide it, and the calculator does the work. Here’s how:

1. Note the current in amps.
2. Measure the one-way distance. The calculator doubles it, because current goes out on the positive and back on the negative.
3. It keeps voltage drop to Victron’s 2.5% target (0.3V on 12V) and applies Victron’s short-run rule (cable area in mm² at least the current divided by 3), then gives you the thicker of the two.
4. Check the cable maker’s ampacity rating for that gauge is above your fuse size.

On a boat, use tinned, fine-strand marine cable.

Wire gauge calculator

Round trip. The current runs out on the positive and back on the negative, so voltage drop is lost on both. Measure the one-way run from battery (or busbar) to the device, and the calculator doubles it for you.

Wire gauge calculator

Yes, as long as the two cables together have at least the cross-section the single cable would need. Victron’s example: two 35mm² cables equal one 70mm². Both cables need the same length and the same lugs, and each still has to be protected properly.

Wire gauge calculator

The fuse protects the wire, so size it to the wire. Here’s how:

1. Pick a fuse rated above the device’s normal current.
2. Keep it at or below what the cable can safely carry (the cable maker lists that).
3. Give every device its own fuse on the positive, close to the power source.
4. With lithium, make sure at least one fuse in the line has an interrupt rating at or above the battery’s maximum short-circuit current (the battery maker publishes it). Class T fuses are made for that. Check an ANL fuse’s interrupt rating too: Victron’s wiring book lists a Blue Sea ANL at 6,000A.

If anything’s unclear, have a marine or RV electrician look before you power up.

On the positive cable, as close to the battery’s positive post as you can get it. Everything between the battery and that fuse is unprotected, so keep that run as short as possible. The battery switch comes after it, then the positive busbar and the fuse blocks.

Get a shunt rated above the most current that will ever flow through it. Here’s how:

1. Take your biggest load (an inverter pulls about its watts divided by 12 at 12V) plus anything else on at the same time.
2. Compare that with your biggest charger, and use whichever is higher.
3. Pick the next shunt size up. Victron makes the SmartShunt in 300A, 500A, 1000A and 2000A; we carry the 500A, the 500A IP65 and the 1000A. The BMV-712 comes with a 500A shunt.

Battery monitor picker

Match the controller to your panel watts and voltage. Here’s how:

1. Read the name: in an MPPT 100/30, 100 is the highest panel open-circuit voltage it takes and 30 is the most amps it charges with.
2. Cover your panel watts. Victron rates the 100/30 for 440W of panels on 12V and the 100/50 for 700W.
3. Keep your panels’ open-circuit voltage, wired in series, under the first number. It rises in cold weather.
4. Double-check with Victron’s online MPPT sizing tool for your exact panels.

Solar controller sizer

Use a DC-DC charger between the start battery and the lithium house bank. Victron’s Orion-Tr Smart 12/12-30 is a good fit. It charges the lithium bank at a set current (30A on that model) instead of letting the bank pull whatever it wants from the alternator. A plain battery combiner is made for lead-acid banks, so we don’t suggest it for a lithium house bank. Our wiring diagram guide shows the hook-up step by step.

Not in the same bank. The common setup is a lithium house bank and a lead-acid start battery kept separate, with a DC-DC charger moving engine charge into the lithium side. Our wiring diagram guide shows it.

Both track battery voltage, current and state of charge. The SmartShunt has no screen: you read it on your phone over Bluetooth. The BMV-712 adds a panel display, a programmable visual and audible alarm and a programmable relay that can switch off loads or start a generator. If you want a gauge on the dash or an alarm, get the BMV-712. If your phone is enough, the SmartShunt is less wiring.

Victron says the usual range is 10 to 15 meters. A metal vehicle chassis or seawater around a hull can cut that a lot. If it won’t reach, Victron’s fix is a VE.Direct Bluetooth dongle placed where the signal gets out, with the SmartShunt’s own Bluetooth switched off.

Partly. The SmartShunt’s extra input can read one of three things: the voltage of a second battery, the midpoint of a series bank, or temperature with the optional sensor. So you get the start battery’s voltage, not its full state of charge.

The standard SmartShunt is rated IP21, so keep it dry. For a damp spot, Victron makes an IP65 version of the 500A SmartShunt, which we carry.

Yes. We carry lithium batteries for trolling motors, boats, RVs and vans, plus small packs for ice fishing. Each product page lists the maker and its specs. Some are special order and ship from the maker; the product page says so, and special orders are final sale. Batteries ship by ground, lower 48 states only. The biggest ones go by truck: $300 freight per order, lower 48, with liftgate delivery, added at checkout.

Trolling motor batteries

Check the voltage line on the product page. Some items work on both: the Cyrix-ct is a 12/24V model, and the SmartShunt runs on 6.5 to 70V DC. Others, like our 12V inverters and the Orion-Tr 12/12, are 12V only. If the page isn’t clear, email us the part number and your system voltage.

A busbar is a common point for many cables; the Victron 4-point busbar is rated for 250A. A fuse block gives each branch circuit (lights, pumps, electronics) its own fuse; the Egis RT 12-position block has a ground bar built in. Count your circuits, add a few spares, and match the main feed to the total current.

Match two things: the cable gauge and the stud size. Here’s how:

1. Read the cable size (for example 2/0) and the stud it bolts to (for example 3/8 inch).
2. Get a lug made for both, like a 2/0 lug with a 3/8 inch hole.
3. Crimp it with the right tool for that size and seal it with heat shrink.

Victron lists good lugs, crimped with the right tool, as one way to keep voltage loss down.

It depends on your boat’s length and whether it’s under power or sail, and the rules are in the US Coast Guard Navigation Rules. We can’t tell you what’s legal for your boat, but once you know the lights required, we carry Perko, Hella and Railblaza lights, and each product page shows the maker’s rating for that light.

That part needs a qualified electrician. Anything on the AC side (shore power, a panel, outlets, a transfer switch, an inverter-charger’s AC in or out) is a job for a qualified electrician, and local rules may require a licensed one; on a boat, look for an ABYC-certified marine electrician. AC at 120V can kill, and boats and RVs have their own grounding rules. We’re glad to help you pick the DC side: battery cables, fuses, monitor and charger.

If you smell burning or see smoke, swelling or heat, switch off only if it’s safe, keep clear, and call 911 if there’s fire. Otherwise, start with the simple stuff: a lot of "dead" gear turns out to be a blown fuse or a setting. First switch off the loads, the chargers and the battery switch. The battery itself stays live, so keep tools off its terminals. Then check:

1. Is a fuse blown? If so, find out why before you replace it, and never fit a bigger one.
2. Is a battery switch off?
3. Is a connection loose or corroded?

Error codes are in the maker’s manual, and Victron, Samlex and Egis all have support lines. If you’re still stuck, a marine or RV electrician can take it from there.

Put your order number and email in the order lookup below. It shows the status and, once it has shipped, the carrier and tracking number. We also email tracking once the warehouse ships it.

Order lookup

Orders leave our distributor’s warehouse in 1 to 2 business days and arrive 2 to 5 business days after that, by ground. We email the tracking number as soon as it ships, and the tracking shows the carrier’s delivery date.

Order lookup

$9.95 per order, flat, by ground: one charge per order, not per item. Checkout shows it before you pay. That covers street addresses in the lower 48 states and Washington, DC.

We ship to street addresses in the 48 contiguous states and Washington, DC. We can’t ship to Alaska, Hawaii, Puerto Rico, US territories, APO/FPO addresses or outside the US yet. Please use a street address, not a PO box.

Email us right away with your order number. We’ll try to change it, but once it has left the warehouse we may not be able to. If it has already shipped, you can return it under our return policy once it arrives.

Returns and warranty

Sorry about that. Email us within 7 days of delivery with your order number and photos of the damaged item, the outer box and the shipping label. Keep the box and packing until it’s settled. Once our warehouse opens the carrier claim, we ship your replacement at no charge. You don’t have to wait for the carrier to pay.

Returns and warranty

Email us within 7 days of delivery with your order number and a photo of what arrived and its label. If we sent the wrong item, you pay nothing: no restocking fee, and we cover shipping both ways. Orders can come in more than one box, so check your tracking emails first. If tracking says delivered and you can’t find it, check with neighbors, then email us and we’ll open a trace with the carrier.

Order lookup

Not always. An order can arrive in more than one box, for example if one item ships a few days after the rest, and you still pay shipping once. You get a tracking email for each part. If an item can’t ship within 7 days of your order, we cancel that item, refund it and email you.

Order lookup

Only on orders shipping to California for now. Checkout shows any tax before you pay.

Checkout takes cards through Stripe, and any other options your device supports show up on the checkout page.

You have 30 days from delivery to start a return. Items must be unused, not installed or wired, complete and in the original packaging. Ask us for a return number first. You pay return postage, a restocking fee of up to 15% comes off (exactly what our warehouse charges us), and original shipping isn’t refunded. Special-order items and cut wire or cable can’t come back. If we sent the wrong item or it arrived damaged, you pay nothing.

Returns and warranty

Email us your order number, the item and the reason. Please don’t send anything back yet. We reply with a return number (RMA) and the address, usually within 1 to 2 business days. Write the RMA on the outside of the box and ship it with tracking.

Returns and warranty

Everything we sell is covered by its maker’s warranty; we don’t add one of our own. Each product page shows the length and links the maker’s terms. If something stops working, email us your order number, the product and what it’s doing. A photo or short video helps. We check it isn’t a blown fuse or a setting first, then send you the maker’s claim steps and a copy of your invoice.

Returns and warranty

We refund your card within 2 business days of our warehouse confirming the return, minus the restocking fee (up to 15%). Original shipping isn’t refunded. Your bank may take a few more days to show it, and your refund email shows the exact fee.

Returns and warranty

Yes. Call 831-477-9600 or email [email protected] with your question and your order number if you have one. A person answers anything our helper can’t.