New BEP Digital VSR

One of the world’s top suppliers of marine electrical products, BEP Marine, is introducing a new digital voltage sensitive relay. It replaces the company’s well known VSR, which is hugely popular and is considered essential on any boat with more than one battery bank.

The DVSR, which functions as an automatic smart battery switch…

…allows charging of two independent battery banks from a single charging source. When the voltage on the start battery rises to a charged level, the DVSR engages allowing the 2nd battery to charge. When charging stops and voltage falls, the DVSR will disengage, isolating the two batteries from each other. Dual sensing functionality enables the sensing of two battery banks, allowing two way charging.

Here is an earlier post from our site explaining the VSR in detail.

According to BEP, their new DVSR offers a number of advantages over the older version. They include:

  • 80% lower stand-by current draw during normal operation when powered but disengaged
  • Zero stand-by current draw when remote sensing circuit utilized
  • Multi voltage – auto selects between 12V and 24V DC operation
  • Remote status LED output. Provides DVSR status indication at remote location
  • Remote sensing circuitry provides isolated control from secondary supply, and enhanced protection from voltage spikes when connected to ignition switch
  • Increased accuracy of voltage measurement through digital circuitry
  • Lowered cut in voltage from 13.7V to 13.4V (26.8V for 24V) to suit low output alternators, and high temperature environments

Boaters who want to upgrade to the new BEP DVSR will find it on our sister boat wiring site, EzAcDc later this summer.

Adding a third boat battery

Hi Kevin,

My boat is a 2005 Sea Ray Sundancer with a single 8.1 liter engine.

I currently have two boat batteries and would like to add a third. I’m not sure how to accomplish this as my marine battery switch is only set up for two batteries.

Is it possible to tie two of the batteries together? If I did would they still charge properly? I’ve looked at
marine electrical isolators but not sure if thats what I need either.

Any suggestions?



Hi Dewayne,

If your goal is to simply add battery capacity to your boat accessory battery, then you can add the third battery by running a ground cable to connect the grounds and a positive cable to connect the positives. I recommend keeping the length to a minimum and using at least the same size wire as the current boat battery cables.

If you are looking for third, separate battery bank, then I would recommend either using an isolator or voltage sensitive relay, a VSR. VSRs are easier to install and more reliable.

Hope this helps,




If I connect two boat batteries together for extra capacity, will the batteries still charge adequately via the charger/alternator?


Hi Dewayne,

Yes they will, but it will take longer for them to fully charge.



I really appreciate the input. I recently installed a larger amp for my stereo and it’s draining my boat’s house battery when I stay out at anchor overnight.

My battery charger will charge up to 3 separate banks. Eventually I’ll figure out how to wire all three separately. Just looking for a relatively easy fix without getting too complicated.

Thanks again!


Clearwater Boat Wiring – Part 2


Here is a boat wiring diagram for the marine electrical on my 2008 Clearwater 2200WA with a 225HP Yamaha.

I have a two battery configuration where one is used for starting and the other is the house battery for electronics and the like. I have both boat batteries connected via a dual circuit marine battery switch (5511e) and both batteries are charged via isolated leads from the outboard since this outboard provides an accessory charging lead in addition to the primary lead to the starting circuit.

I keep both batteries off via the battery switch when the boat is not in use and the only direct wiring to the battery is for the bilge pump float switch.

The other day, I could not start the motor because of a discharged starting battery after the boat had sat for several days. I switched to the combine mode and the motor started. Ran all day with no issues.

Two questions, please: Is there a problem with the boat battery wiring or charging circuit? Will this circuit accommodate a battery charger if the boat battery switch is in the off position?



Hi Frank,

This is a great marine electrical system and the dual circuit PLUS battery switch is one of the key components. My best guess on the dead battery would be the device that is connected to the mystery red lead connected to your starting battery (at the switch). It is probably a stereo memory wire or some type of memory device.

With the switch in the off position, you will need to use a dual output battery charger or manually connect your charger to one battery and then to the other. If you are installing a dual output charger, I strongly recommend connecting the battery at the switch and your ground bus and not at the battery. Too many battery connections become confusing and the mix of small and large wires on the terminals always causes a loose connection.

Hope this helps and nice wiring diagram,


Hi Kevin,

Me again.

Still having trouble starting the motor with the starting battery. Now sits overnight and unable to start a cold motor in the morning. Does not seem to turn fast enough.

When the selector switch is set at COMBINE, starts right up. The mystery red wire you refer to is at the switch and I don’t think it could drain the battery since the switch is in the OFF position overnight.

Any other thoughts?



Have you load tested the starting battery? Most auto parts stores do this for free.

If it is not the battery:

  • Using a digital voltmeter, look at the starter voltage while trying to start your cold engine. Try it with the battery switch in the on position first and then the combine.
  • It could be something as simple as a bad ground cable or corroded battery lug connection. Shrink tube covered cable connections are great but they can also hind bad connections.
  • It could be a combination of battery cable size and battery age.

You are close to figuring it out. All loads are disconnected so it comes down to connections, cables, and batteries.

Let me know what you find out


House Battery Bank

Hello Kevin,

Thanks for all of your really helpful boat wiring advice.

I am rebuilding my boat battery wiring to add a dedicated house battery system.

I want to use six 6 volt lead acid batteries and want to wire them in a series/parallel configuration – but am confused about how each battery is inter-connected with the one next to it. They will sit in two rows of three batteries each.

Would you have a boat wiring diagram showing how to wire this up for six marine batteries?



Hi Charles,

Dedicated house battery systems are becoming more popular in marine electrical and for good reason. They can really help with power management and – more importantly – can make sure that you can start your engines to get home after a long day playing. This is especially true of boat battery wiring that includes an automatic smart boat battery switch.

Here is a boat wiring diagram that should help your with your project.


Wrong Charger?

Hi Kevin,

I hope you can help me with a boat wiring issue.

On my boat battery wiring, I have two batteries for my trolling motor, a 24 volt Motorguide. They are hooked up

  • + to motor
  • – on battery to + on 2nd battery
  • – to trolling motor

The on board marine electrical battery charger has connections for two batteries. Do I just hook it up positive and negative on both batteries?

The reason I ask is the in line fuse on one battery was blown as I took it apart today.



Hi Dean,

Most dual output battery chargers are designed to be connected the way you had them.

The blown fuse may just be a fluke or your charger may not be designed to charge your batteries in series. Check with the manufacturer’s recommendations. If they say 12/24 volt systems, then you are good to go. If not, you will need to disconnect the batteries to charge or buy another charger.