What is the BATT BOOST switch on the dash

[AlwaysDream]

2025 Jayco Entegra 29S Class A Gas Coach

What does the Batt(ery) Boost Switch do?
How does it Work
If it connects the vehicle battery to the House Battery, how long do they stay connected?

Context:
I have a suspected drop in voltage due to 2 refrigerators surge current upon turning on. Could the Battery Boost switch help hold the voltage up during this time?

Thanks for reading

[dvspl]

Originally Posted by AlwaysDream

2025 Jayco Entegra 29S Class A Gas Coach

What does the Batt(ery) Boost Switch do?
How does it Work
If it connects the vehicle battery to the House Battery, how long do they stay connected?

As you suspected, it ties the chassis battery to the coach battery through a solenoid. The solenoid closes automatically whenever the engine is running and allows the alternator to charge the coach battery. It opens when the engine is off unless you push the boost switch button. In that case it stays closed as long as the button is held. This is typically done to use the coach battery to boost the chassis battery for engine start if the chassis battery is low. You hold it in for a few minutes to pass some charge to the chassis battery, then hold it in while you start the engine. I'm not sure that it will help much in your situation but just starting the engine before you turn on the fridges will close the solenoid and provide additional alternator power.

[d23haynes57]

The boost switch-relay combines both battery banks to help get eighter the engine or generator started should one set get too low to do that. Normally they are momentary. You hold it while trying to start the engine. On some rigs it is maintained as that is the means to charge the chassis batteries from the house charging system.
Why do you have 2 refrigerators? You likely do not have enough battery or since this a new rig the batteries may have been abused and are damaged. This is a common problem. Do you have battery load monitoring? Power-current in and out and calculated state of charge. Often referred to as shunt meters. Relying on batteries for refrigeration this is a must have.
I would suggest that the batteries be load tested and that find your demands and capacities. For lower end rigs it is common that you have just enough battery capacity to get through a partial day relying on generator and park power. You may need to do some upgrades. You don't want to share the loads across the house and chassis batteries as that can leave you stranded with both dead. Also, chassis batteries are not designed and do well for cycling applications.

[AlwaysDream]

Originally Posted by dvspl

As you suspected, it ties the chassis battery to the coach battery through a solenoid. The solenoid closes automatically whenever the engine is running and allows the alternator to charge the coach battery. It opens when the engine is off unless you push the boost switch button. In that case it stays closed as long as the button is held. This is typically done to use the coach battery to boost the chassis battery for engine start if the chassis battery is low. You hold it in for a few minutes to pass some charge to the chassis battery, then hold it in while you start the engine. I'm not sure that it will help much in your situation but just starting the engine before you turn on the fridges will close the solenoid and provide additional alternator power.

Thank you for the reply.

My issue is during No Shore or Generator AC Power. This operational mode is used a couple times a year while infield camping at Sebring or Daytona, where I don't want to run the generator overnight.

My problem is the refrigerators "on/off" are under temperature control so they will "surge current" on a few times overnight, with the remote possibility that they turn on (surge current) simultaneously which is worst case. What happens is the Xantrex 1200 Watt inverter does a Low Voltage Shutdown due to what I suspect is refrigerator surge current when the compressors start causing the Voltage to drop below 10.2 Volts. Per your explanation, the while on the road, the solenoid is closed and the alternator can supply the surge current. The Inverter has never done a Low Voltage Shutdown while the engine is running or when the generator is running or on shore power.

One possibility would be to change the Battery Boost to a Toggle Switch so the Chassis and House battery stay connected (for a few hours) to handle the refrigerators start up surge currents.

Do you think connecting the Chassis and House batteries with the engine off (i.e. alternator off) would hurt either battery if the solenoid is closed for 6 hours?

Both the House and Chassis batteries are sealed lead acid. Assume the batteries start fully charged at bed time.

What do you think?

A different solution might be to wire in a Hold Up Capacitor. Any thoughts on this?

As always, thanks for reading.

[d23haynes57]

Originally Posted by AlwaysDream

Thank you for the reply.

My issue is during No Shore or Generator AC Power. This operational mode is used a couple times a year while infield camping at Sebring or Daytona, where I don't want to run the generator overnight.

My problem is the refrigerators "on/off" are under temperature control so they will "surge current" on a few times overnight, with the remote possibility that they turn on (surge current) simultaneously which is worst case. What happens is the Xantrex 1200 Watt inverter does a Low Voltage Shutdown due to what I suspect is refrigerator surge current when the compressors start causing the Voltage to drop below 10.2 Volts. Per your explanation, the while on the road, the solenoid is closed and the alternator can supply the surge current. The Inverter has never done a Low Voltage Shutdown while the engine is running or when the generator is running or on shore power.

One possibility would be to change the Battery Boost to a Toggle Switch so the Chassis and House battery stay connected (for a few hours) to handle the refrigerators start up surge currents.

Do you think connecting the Chassis and House batteries with the engine off (i.e. alternator off) would hurt either battery if the solenoid is closed for 6 hours?

Both the House and Chassis batteries are sealed lead acid. Assume the batteries start fully charged at bed time.

What do you think?

A different solution might be to wire in a Hold Up Capacitor. Any thoughts on this?

As always, thanks for reading.

You mention refrigerators! You have more than one? What size? And on a 1,200 watt Inverter.
Using the boost to get you through the night can leave you with 2 sets of batteries that are too low to get the engine or generator started. Is there any room to add another House battery? Another option is to upgrade to lithium. Lithium does a much better job at supporting surge demands and can deliver more usable power for a given capacity.

[followingsea]

Originally Posted by AlwaysDream

Thank you for the reply.


Do you think connecting the Chassis and House batteries with the engine off (i.e. alternator off) would hurt either battery if the solenoid is closed for 6 hours?

Both the House and Chassis batteries are sealed lead acid. Assume the batteries start fully charged at bed time.

What do you think?

I think you should not do it. It is one of those cases of 'if you have to ask. don't do it.'

It takes a lot of experience dry camping to figure out managing your batteries.

When my propane RV frig died, I replaced it with a residential frig. The starting current would trip the inverter in the middle of the night.

I found that the residential frig would stay cold until morning when turned off after running the generator during evening chores.

[AlwaysDream]

Originally Posted by d23haynes57

The boost switch-relay combines both battery banks to help get eighter the engine or generator started should one set get too low to do that. Normally they are momentary. You hold it while trying to start the engine. On some rigs it is maintained as that is the means to charge the chassis batteries from the house charging system.
Why do you have 2 refrigerators? You likely do not have enough battery or since this a new rig the batteries may have been abused and are damaged. This is a common problem. Do you have battery load monitoring? Power-current in and out and calculated state of charge. Often referred to as shunt meters. Relying on batteries for refrigeration this is a must have.
I would suggest that the batteries be load tested and that find your demands and capacities. For lower end rigs it is common that you have just enough battery capacity to get through a partial day relying on generator and park power. You may need to do some upgrades. You don't want to share the loads across the house and chassis batteries as that can leave you stranded with both dead. Also, chassis batteries are not designed and do well for cycling applications.

Thanks for the reply
This coach has a outside galley with a 115V 6 cu-in fridge connected to the Xantrex 1200W Inverter (DC to AC). The indoor galley is a 10 cu. in. DC fridge.
I have a Victron "current shunt" on my House Batteries for monitoring. Steady State monitoring parameters log looks good, within parameters, No alarms. My suspicion is that Voltage drop due to the fridge surge current recovers before the Victron detects it. The Victron inverter will do a low voltage shutdown for a 2 second drop below 10.2 Volts.

I am thinking my Harbor Freight el cheapo DMM won't detect a Voltage dip?

I am not worried about exhausting my DC power while the House and Chassis connected as this config won't be used often and both are all would be fully charged and monitored and only connected for 6 or 7 hours.

However, I like the idea of doubling House Battery capacity better. Currently, I have two 6 Volt deep cycle lead acid sealed batteries in series rated at 200AH.
I could add one 12V in parallel or two 6V (in series) in parallel for even more capacity. I have to see how much space I have.

Your thoughts are appreciated. Thanks

[Unplanned Tourist]

Originally Posted by AlwaysDream

However, I like the idea of doubling House Battery capacity better. Currently, I have two 6 Volt deep cycle lead acid sealed batteries in series rated at 200AH.
I could add one 12V in parallel or two 6V (in series) in parallel for even more capacity. I have to see how much space I have.

Your thoughts are appreciated. Thanks

I would go for the 2 more 6 volt batteries. Then all your charge system will be good as is. No need to upgrade.

[AlwaysDream]

Originally Posted by followingsea

I think you should not do it. It is one of those cases of 'if you have to ask. don't do it.'

It takes a lot of experience dry camping to figure out managing your batteries.

When my propane RV frig died, I replaced it with a residential frig. The starting current would trip the inverter in the middle of the night.

I found that the residential frig would stay cold until morning when turned off after running the generator during evening chores.

My problem is the Xantrex 1200 Watt inverter also runs my 115V AC CPAP machine.

I am thinking that I prefer adding more house battery capacity then the long term connect of Chassis and House Batteries.

Do you think adding more house batteries would have fixed you inverter shut down?
Did you get an error code, what inverter do you have?
Thanks for reading

[d23haynes57]

For AGM Batteries 11 volts at rest is considered discharged. 200 A/H is the bare minimum to support a 1,000 watt inverter and won't do it for long. You really want enough battery to support the load at a 4 hour rate for lead acid or AGM. Do you know what you have for house battery charging control and what size your engine alternator is.
You should be able to drop in one of these.
https://www.amazon.com/ECO-WORTHY-Bl...0DJ2VHKLS&th=1

[AlwaysDream]

Originally Posted by d23haynes57

You mention refrigerators! You have more than one? What size? And on a 1,200 watt Inverter.
Using the boost to get you through the night can leave you with 2 sets of batteries that are too low to get the engine or generator started. Is there any room to add another House battery? Another option is to upgrade to lithium. Lithium does a much better job at supporting surge demands and can deliver more usable power for a given capacity.

Indoor Galley Fridge is DC
Outdoor Galley Fridge is AC and is run be the 1200 Watt Inverter.

Ultimately they both draw DC power off the house battery when no shore or generator.

Lithium is definitely an option. the coach has solar and PD4500 Power Control Center with Charging Wizard. I have to research if my dc charging system can be converted from AGM to LI

Cheapest solution but ill advised and risky - Change Battery Boost "Push and Hold" Switch to a toggle switch and leave the solenoid on so chassis and house DC is connected. Would need to research and experiment. I would also carry on of these as a backup. They say they work?
Jump Box Car Starter

No risk, but expensive - double AGM Batteries to 400 AH

Most Expensive - Switch to LI 400AH Battery Bank, convert Charging System to LI

I still need to do a power calculation spreadsheet from the Manufacture's Spec Sheet.

Thanks to all

[d23haynes57]

Originally Posted by AlwaysDream

Indoor Galley Fridge is DC
Outdoor Galley Fridge is AC and is run be the 1200 Watt Inverter.

Ultimately they both draw DC power off the house battery when no shore or generator.

Lithium is definitely an option. the coach has solar and PD4500 Power Control Center with Charging Wizard. I have to research if my dc charging system can be converted from AGM to LI

Cheapest solution but ill advised and risky - Change Battery Boost "Push and Hold" Switch to a toggle switch and leave the solenoid on so chassis and house DC is connected. Would need to research and experiment. I would also carry on of these as a backup. They say they work?
Jump Box Car Starter

No risk, but expensive - double AGM Batteries to 400 AH

Most Expensive - Switch to LI 400AH Battery Bank, convert Charging System to LI

I still need to do a power calculation spreadsheet from the Manufacture's Spec Sheet.

Thanks to all

The battery I recommended is on sale, $375 after coupon. It will work drop in.
If you want a bit more power and match 4 golf cart AGM go for 2 of these.

https://www.amazon.com/Litime-LiFePO...d_i=B0BYH8J176

There is also the Bluetooth version.

https://www.amazon.com/Litime-Blueto...0DLB1ZVDK&th=1

These directly match the GC sets in theory capacity but actually deliver much more.
If your system can handle the 4 GC AGM set it will handle these 2 as drop in.
The BMS will take care of charge cut off and balance. These are also compatible with AGM being connected with the chassis batteries for engine alternator charging.

[followingsea]

Originally Posted by AlwaysDream

.....
Do you think adding more house batteries would have fixed you inverter shut down?
Did you get an error code, what inverter do you have?
Thanks for reading

No, your problem is starting current not battery capacity.

I have a 2000 watt Trace inverter and 4 GC2 batteries. My error code was the television turning off at the same time the frig clicked on.

I was a KISS engineer at power plants. I suggested a solution with zero cost and no work. You might try it!

Since you have an outdoor fridge and go to NASCAR in your RV, you might be a work harder not smarter type of guy.

I used to be a work harder type of guy. When I was enlisted in the navy it got me into an officer program. There came a time I was going to fail because working harder was not getting it done. So I figured out how to work smarter.

Sitting in the dark with the boob box off, gives you time to think.

I turned off the fridge and turned on the boob box. The next morning the temperature was fine. I started the generator and turned the fridge back on.

One suggestion for keeping the fridge cold is keep it full of MGD. The beer bottle cap works great for keeping the boost switch on. Bottle cap = KISS BIRD complicated.

[AlwaysDream]

Originally Posted by followingsea

No, your problem is starting current not battery capacity.

I have a 2000 watt Trace inverter and 4 GC2 batteries. My error code was the television turning off at the same time the frig clicked on.

I was a KISS engineer at power plants. I suggested a solution with zero cost and no work. You might try it!

Since you have an outdoor fridge and go to NASCAR in your RV, you might be a work harder not smarter type of guy.

I used to be a work harder type of guy. When I was enlisted in the navy it got me into an officer program. There came a time I was going to fail because working harder was not getting it done. So I figured out how to work smarter.

Sitting in the dark with the boob box off, gives you time to think.

I turned off the fridge and turned on the boob box. The next morning the temperature was fine. I started the generator and turned the fridge back on.

One suggestion for keeping the fridge cold is keep it full of MGD. The beer bottle cap works great for keeping the boost switch on. Bottle cap = KISS BIRD complicated.

Thank you
I am not a serious NASCAR fan, but rather I am a IMSA (International Motor Sports Association) fan. They run the Endurance Racing Circuit, 24 Hours At Daytona, 12 Hours at Sebring, 24 Hours of Le Mans (France). Sebring is a road course on an WWII Air Field. They race at night, in any weather with 4 classes of race cars each with different spec limits, so there is a ton of traffic problems which makes the racing very interesting. Sebring is known as the toughest, most aggressive road course in the world.
Here is a link to a 20 minute YouTube on the race last Saturday.

2025 IMSA Sebring

What I really need the Inverter to stay up for is my CPAP at night. I suppose I could leave the refrigerators off at night. I will try that.

Does anyone have any warnings about leaving the Batt Boost on (i.e. Tying the House and Chassis Battery together over night?

I understand the potential of draining both batteries.
However the steady state load is around 350 Watt, which 29 Amps. At 200 Amp Hours, I estimate over 8 hours, not considering the Chassis Battery and considering a 50% duty cycle on the refrigerators. It that correct? I will get the actual Steady State Load for my application with the fridges on and off.

My career was a Electronics Test Engineer in Military and Aerospace. I am a big believer in KISS (Keep It Simple Stupid) but I am not familiar with BIRD?

Thanks for reading