Egis XD FLEX 2 Single VSR Battery Switch with Knob, 500A

The Egis XD FLEX 2 Single with VSR is a marine battery switch that does two jobs in one compact housing. Turn the knob and you get manual on and off control of a high-current circuit. Set it to VSR and it watches your charging voltage, then automatically combines your start and house banks when the alternator or charger comes up, and splits them again when the engine's off. That's the whole point of a voltage sensitive relay. Keep your starting battery topped off without having to remember to flip anything.

It's rated for 500 amps continuous and 1500 amps of cranking current, so it's comfortable sitting between a decent house bank and the starter on a gas inboard or a good-sized outboard rig. The operating range runs 8 to 36 volts DC, which means it drops straight into 12-volt and 24-volt systems without a second thought. Whether you're wiring a center console with a single battery and a house pack, or a sportfisher running twin banks, the FLEX 2 handles the switching duty.

Egis has been building vehicle and marine electrical gear for over 25 years, and this unit shows it. The whole thing measures 3.15 inches long by 2.59 wide by 1.96 tall, so it tucks into a battery box lid or a switch panel without eating up your whole console. The connections use tinned wire terminations, which is exactly what you want in salt air where bare copper turns green in a season. Mounting and terminal hardware is stainless steel with self-locking nuts.

A few install notes from folks who've wired these. Feed it with cable sized to the load. At 500 amps continuous you want 4/0 lugs on the main runs. Undersized 2/0 will heat up under a hard pull, and heat is the enemy of any connection. Give the stainless hardware a thin coat of dielectric grease when you land your lugs, and hit it again once a season. Stainless resists corrosion beautifully, but it can gall and seize if it's left dry for years. And keep an eye on those self-locking nuts after a couple hard seasons of vibration. A dab of thread locker or a fresh nylock is cheap insurance against a loose 500-amp connection.

One number worth understanding is the 1.3 amp off-state current draw. That's the relay's own appetite while it sits there sensing voltage. On a boat that gets used every week or lives on shore power, it's a non-issue. But if you leave a boat on the hook or on a trailer for weeks at a time with no charge source, that draw will pull a house bank down over time. The simple fix is a battery master switch or disconnect upstream, so you can kill everything when the boat's put away. Plenty of boaters run exactly that setup and never think about it again.

The VSR combining logic pairs nicely with matched lead-acid or AGM banks, which is the most common setup out there. If you're running lithium with its own battery management, you'll typically want a dedicated charging strategy and an external regulator in the mix, since lithium's flat voltage curve doesn't give a plain voltage-sensing relay much to work with. For the vast majority of gas-inboard, outboard, and sterndrive boats running conventional batteries, the VSR setting is set-and-forget.

Built to take real marine conditions, the FLEX 2 carries an operating temperature range of -40 to 105 degrees Celsius. That covers a hot engine compartment in July and a trailered boat in a northern winter. The rotary knob gives you a positive, mechanical feel. It can be a touch stiff in the cold when you first turn it, which honestly is a sign the detents are doing their job and the switch isn't going to walk out of position underway.

Who's this for? Anyone who wants automatic dual-battery charging without a rat's nest of manual switches, and who still wants a real knob they can grab to combine banks for an emergency start or isolate a bank for service. It's a clean, single-circuit solution. If you need to manage more circuits, look at the rest of the XD FLEX family, but for a straightforward start and house combine on one boat, this single unit is all most rigs need.