2025 252SD Float Mode and Battery Question

[Signia]

New 2025 252SD, second time on the water today. First time I had it in float mode. Working fine and then I switched off the start battery and the connext screen lost power and then started to go into reboot loop until I turned the start battery back on. Do I need to have the start battery turned on for float mode?

 

[Neutron]

New 2025 252SD, second time on the water today. First time I had it in float mode. Working fine and then I switched off the start battery and the connext screen lost power and then started to go into reboot loop until I turned the start battery back on. Do I need to have the start battery turned on for float mode?

I never turn my batteries off while on the boat. There really is no reason to turn off the start battery. House systems are seperated and wont drain your starting battery unless the parallel switch is on. Plus not having your starting battery on could be a problem if for some reason an emergency comes up and you forget

 

[Signia]

Got it thank you!

 

[Neutron]

Got it thank you!

Your welcome

 

[FSH 210 Sport]

From page 39 in your owners manual

You boat is equipped with a DVSR or digital voltage sensing relay as part of the BEP marine battery switch. When the voltage on both the house and start batteries are at or below 12.7 volts the DVSR keeps the start and house batteries isolated from each other. When you start the engines all of their alternator output goes into the start battery, when the voltage reaches 13.2 volts the DVSR closes a switch that parallels the start and house batteries allowing the engines to start charging the house battery as well. After turning off the engines the DVSR will leave the batteries paralleled until the voltage drops to 12.7 then the DVSR will open the switch isolating the start and house batteries. This keeps the start battery fully charged and ready to start the engines while the house battery discharges . A beautiful set up.

If you do not yet have an onboard battery charger installed that should be at the top of your priority list, especially with your boat having the electric steering and DriveX . Most of the issues I’ve seen on here with boats that have the electric steering are from batteries that are not fully charged, this causes a fault code to get thrown. The alternators on our boats are not very powerful, approximately 14 amps per engine, and flooded lead acid and AGM batteries take a long time to charge due to the absorption cycle. Lead acid batteries whether flooded or AGM need to be re charged as soon as you get back to the dock or home as leaving them in a state of partial discharge damages them.

The NOCO charger is quite popular with folks on this site, be sure you get a 10A per battery charger.

NOCO - 2-Bank 20A On-Board Battery Charger - GENPRO10X2

The GENPRO10X2 is a 2-bank 20-amp waterproof on-board battery charger for lead-acid and lithium batteries and rated at IP68.

no.co

NOCO also makes a really cool AC port. NOCO - AC Port Plug - GCP1EX

A lot of people have also modified their DVSR so that it only becomes operational when the house or start battery switch is turned on, this allows the on board battery chargers to charge the start and house batteries independently so that these batteries get charged properly. Others have set up the DVSR so that it becomes operational only when the engines are on. These modifications are optional set ups with the BEP Marie battery switch and are quite easy to do…lots of help is available to you here on this site. Either way, get an onboard charger in your boat and leave it plugged in while the boat is not in use, your batteries will perform as best they can and will last longer.

 

[ahenderson432]

New 2025 252SD, second time on the water today. First time I had it in float mode. Working fine and then I switched off the start battery and the connext screen lost power and then started to go into reboot loop until I turned the start battery back on. Do I need to have the start battery turned on for float mode?

Same for 2024 255XD. The Connext Screen must have the Start and House Battery on to operate. Talked to my Dealer and verified all wiring is correct and this is the normal operation. With the Parallel switch for backup just don't let the House battery run out. I watch the volts on the Connext throughout the day while floating.

 

[FSH 210 Sport]

Same for 2024 255XD. The Connext Screen must have the Start and House Battery on to operate. Talked to my Dealer and verified all wiring is correct and this is the normal operation. With the Parallel switch for backup just don't let the House battery run out. I watch the volts on the Connext throughout the day while floating.

I’m curious… regarding the start battery, what is the voltage before you start the boat and how much does it drain during a full sandbar day on the water? Might as well ask the same question of the house battery too.

I’m pretty sure that you have a Victron smart shunt for your house battery if memory serves, how many Ah and KWh do you typically see used during a typical outing and what was the most?

Thanks!

 

[ahenderson432]

I’m curious… regarding the start battery, what is the voltage before you start the boat and how much does it drain during a full sandbar day on the water? Might as well ask the same question of the house battery too.

I’m pretty sure that you have a Victron smart shunt for your house battery if memory serves, how many Ah and KWh do you typically see used during a typical outing and what was the most?

Thanks!

I have never dropped below 11 volts on the Connext before running the engines. Run the stereo for a few hours with minimal drop. Not sure on KWh burt am upgrading to 125 Ah Lithium batteries. Will run some tests once I have those installed.

 

[FSH 210 Sport]

Please keep us posted on the 125Ah LFP batteries.

 

[TommyMcK]

I’m curious… regarding the start battery, what is the voltage before you start the boat and how much does it drain during a full sandbar day on the water? Might as well ask the same question of the house battery too.

I’m pretty sure that you have a Victron smart shunt for your house battery if memory serves, how many Ah and KWh do you typically see used during a typical outing and what was the most?

Thanks!

My 255XD is pretty much the same as the 222XD. Fully charged, the Connext shows low 11s on both batteries initially when you first throw the switches as the system is firing up, and low 12s after about 10 seconds or so (there presumably is a larger current draw as the boat initializes itself). The house battery always shows a couple of tenths less than the start battery when the engine is off because the current draw is higher. Draw on the start battery while the engine is off is negligible. I assume that the logic behind having the start battery power the Connext screen is that you want to be able to operate normally / see the display when the house battery is dead.

 

[FSH 210 Sport]

My 255XD is pretty much the same as the 222XD. Fully charged, the Connext shows low 11s on both batteries initially when you first throw the switches as the system is firing up, and low 12s after about 10 seconds or so (there presumably is a larger current draw as the boat initializes itself). The house battery always shows a couple of tenths less than the start battery when the engine is off because the current draw is higher. Draw on the start battery while the engine is off is negligible. I assume that the logic behind having the start battery power the Connext screen is that you want to be able to operate normally / see the display when the house battery is dead.

On my boat, the connext voltage always reads lower than what it really is. I found this out one day when I was using my Fluke 77 multimeter and the Fluke meter indicated .5 volts higher than the connext screen voltage. Since my Fluke meter is 30 years old I took it to the local electronics shop and those guys test it against their new meters on known low DC voltage and my 30 year old Fluke 77 read the exact same as three of the shops meters. My friend said he thought this could be due to voltage drop across a zener diode in the connext screen so just started adding .5 volts to what I saw on the connext screen. However, once the voltage reaches 14.2-14.4 on the connext when the engines are running, the connext and Fluke read the same. Now that I’ve added a Victron Shunt to my house battery and have the aux / start battery tap attached to the start battery, I can these voltage discrepancies in real-time as the smart shunt voltage reads the same as my fluke.

All that to say it’s entirely possible the voltage you are seeing on your connext screen that’s in the low 12’s could be .5 volts higher.

 

[DSG!]

My 2023 275 SDX exhibits the same behavior. How are your running voltages?

 

[FSH 210 Sport]

My 2023 275 SDX exhibits the same behavior. How are your running voltages?

While I’m cruising and the batteries are charged 14.2-14.4 on the connext and the smart shunt… I think it’s important to mention that I keep my boat plugged in when not in use so the batteries are fully charged when I hit the water. My start battery is an AGM group 24, house battery is a 100Ah Battle Born lfp battery..

 

[TommyMcK]

On my boat, the connext voltage always reads lower than what it really is. I found this out one day when I was using my Fluke 77 multimeter and the Fluke meter indicated .5 volts higher than the connext screen voltage. Since my Fluke meter is 30 years old I took it to the local electronics shop and those guys test it against their new meters on known low DC voltage and my 30 year old Fluke 77 read the exact same as three of the shops meters. My friend said he thought this could be due to voltage drop across a zener diode in the connext screen so just started adding .5 volts to what I saw on the connext screen. However, once the voltage reaches 14.2-14.4 on the connext when the engines are running, the connext and Fluke read the same. Now that I’ve added a Victron Shunt to my house battery and have the aux / start battery tap attached to the start battery, I can these voltage discrepancies in real-time as the smart shunt voltage reads the same as my fluke.

All that to say it’s entirely possible the voltage you are seeing on your connext screen that’s in the low 12’s could be .5 volts higher.

I'd generally agree that the value displayed isn't a proxy for the voltage at the terminals of the battery under all conditions. I'd be surprised if the actual digital conversion is done within the Connext (it's probably someplace closer to the battery and sent via CAN message) but wherever it is happening, it isn't the same thing as reading the at the battery terminals in isolation with no current draw (which is really the only way that you'd want to infer the state of charge from a voltage measurement). We'd need a real schematic to fully explain what we are seeing on the display. But based on your observation, some current is flowing somewhere prior to the measurement conversion that varies as the batteries charge while the magnetos and regulator are active. I'll have to refamiliarize myself with your shunt configuration. I remember thinking it was cool, but that is about all.

My main point though was that even if the Connext was accurately showing the voltage at the terminals of the battery in real-time, it doesn't mean much because the battery terminal voltage is a function of the current draw from the battery, and we don't know what that is as the boat goes through its various startup phases. Some folks were concerned that their battery is toast because the display sometimes reads in the 11's, but there isn't necessarily anything wrong with that when the battery is under load and not being charged.

 

[DSG!]

I have the service manual, but it isn’t clear how the charging works to sample alternator output when running. Is there a pointy to measure regulated voltage output?

 

[FSH 210 Sport]

I have the service manual, but it isn’t clear how the charging works to sample alternator output when running. Is there a pointy to measure regulated voltage output?

Not that I know of.

The rectifier / regulator is a stand alone full wave unit that turns the three phase AC voltage into DC voltage and the regulator shunts unwanted voltage / current to ground as our alternators are the permanent magnet type and are always at full output. It’s a typical charging set up for power sports equipment, simple and compact.

The Victron Energy smart shunt is installed with the house battery ground attached to one side and the system ground on the other side so it can measure all current going into and out of the house battery, as well as measuring voltage on the house battery.

SmartShunt - Victron Energy

The SmartShunt is an all-in-one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the...

www.victronenergy.com

https://www.victronenergy.com/upload/documents/Datasheet-SmartShunt-IP65-EN-.pdf

That’s the closest you will get to watching current flow in either direction, you can accurately measure system loads as well as seeing how much current your alternators are putting into the battery as well as the state of charge of the battery that gets updated in real time as the alternators or battery charger puts power back into the battery.

Also, as the literature states, if you want audible alarms then a 712 model display will have to be installed. But, you can configure the app to show a visual alarm when you check status on your phone. There are updates to the firmware of the app and devices.

 

[anmut]

FYI - I installed one of these last year in place of the passenger side factory USB outlet. Plug & play installation, plus gives you a higher charging rate for the newer phones. I found the voltage shown here (direct from the battery) to be within +/- .1v of what Connext was stating for voltage when we were at the sandbar.

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