We have a Winn 2007 Voyage. We camped recently plugged in at a state park. My DW used the driver's seat to do her cross-stitching and used the driver's dome light over her shoulder. Well when we got ready to leave the MH wouldn't start - click click click. I now realize that the driver's dome light is likley on the engine battery not the converter or house batteries so assume it drained the engine battery. No worries, I will use the battery boost switch. Well, I held the boost switch in and it made zero difference - click click click. I tried several times with no luck. Thankfully we had towed our Jeep, had jumper cables and we were able to jump start the engine and get home. I replaced the engine battery 2 yrs ago, the cells have sufficient water. Any ideas what my problem might be? - Is the boost solenoid bad? How do I check it? - Am I supposed to hold the battery boost switch for several minutes before I try to start? - Is the power for the battery boost switch from the engine battery or the house batteries?- other?Any advice how to trouble shoot would be appreciated. If MH is not dependable my wife gets nervous that we will get stuck somewhere, me too for that matter!Many thanks....

If you hear the relay click, you are getting control power to it.You need to locate the relay, then check each side with a volt meter. They may not read the same or should not read the same.There should be chassis battery voltage on one side and coach battery power on the other. This is on the large terminals. If no power is seen on one of the terminals there is an open conductor or bad connection between it and the associated battery. Then have a helper hold the switch in to operate the relay. The relay large terminals should read the same. If not the relay is bad.

Don't know the wiring of your coach, but it is possible that voltage to activate the boost switch comes from the chassis battery. If so, and the chassis battery is dead, there may not be enough voltage to close the boost relay.If this is the case, use a jumper wire (small gauge is fine-- you will be powering less than one amp) from the house battery terminal of the boost solenoid to the positive signal terminal (will be a small wire/terminal). Once both banks up, you can check the solenoid, and it should be working (again, if my speculation above is correct). If you need advice on how to verify it, let us know.Long term, you need to make arrangements for the chassis battery bank to be charged (assuming this was not OE).

If you have an opportunity to try starting using jumper cables from the house battery to the chassis battery, try that. Your boost switch might be working fine, but you could easily have a weak connection in the heavy wiring from house batteries to the boost switch, and then on to the chassis battery. Using the jumper cables and seeing it that makes a difference will give you a clue or two where the problem might be.When using the jumper cables, first just connect the positive to positive. If it starts, the positive line is the problem and your ground is good. If not, then connect the negative cable only. If it starts, your ground connection is the problem, and the boost switch is working properly.

Hi,To prevent this from happening again add a Trik-l-Start so the chassis battery will charge from the converter.

I don't know how it works on all coaches, but on my bounder - my generator starter is much smaller than the truck. If I crank the generator on first, it supplies just a bit more power to the batteries and sometimes can crank the engine rather than just hearing a click. On my other Class C (Toyota) this does not work like that. I have to run the generator giving a fresh charge to the house bats, turn it off, then sometimes it will give enough "fresh juice" for the truck to start.

Battery Boost Not Working | Good Sam Community

15 Replies

Ivylog
Explorer III
Jan 13, 2015
OP, you may have to hold the boost on for several minutes if the engine batteries are way down. The contacts in my boost relay are as big as the contacts in most starter relays but like Macktee they get corrosion from lack of use and arcing which keeps them clean. You are not going to wear them out from using it plus it's probably the relay that lets your alternator charge your house batteries.
Macktee
Explorer
Jan 13, 2015
Just took the relay apart on this 2004 Monaco and it had a lot of corrosion in it. cleaned it up real good, put it back together and voila, I could use the boost again and now had charge on coach batteries while driving down the road. Macktee
enblethen
Nomad
Jan 12, 2015
Many rigs use the same relay for charging the coach battery from the rig's alternator.
Yes, it is important to energize the auxiliary start prior to attempting to start the rig. The arcing can cause early failure of the relay contacts.
wolfe10
Explorer
Jan 12, 2015
jerseyjim wrote:
When new (2001) the RV mechanic told me not to use the "boost" at all....something about a relay or something else having a habit of blowing out.

Particularly on coaches that require a LOT of starting amps (like diesel coaches with intake manifold heaters) common advice is to ALWAYS use the boost switch if the house batteries are fully charged to put all the amp-hrs possible into the heater and starter.

BUT, the proper sequence IS IMPORTANT to solenoid longevity:

Engage boost switch BEFORE turning the key-- that way you are not switching under high amp load. If you were to engage boost after turning the key, you would arc the contacts and absolutely would shorten solenoid life.

Start engine. After starting, and after intake manifold heater kicks off if diesel engine, THEN turn off boost switch.
jerseyjim
Explorer
Jan 12, 2015
When new (2001) the RV mechanic told me not to use the "boost" at all....something about a relay or something else having a habit of blowing out.

So...once I used it. Guess what? The solinoid clicks...but nothing happens. Guess that one time I used it...or tried to....I guess something y'gotta LISTEN to the mechanic.

No matter...if the 12V battery cannot start the motor, I do two things: If I am on shore power (like when snowabirding) and the 12V battery winds down due to not being charged for a couple/three months....I simply put a battery changer on it overnight to change it up.
Otherwise, in a hurry, jumper cables (from the toad, for instance) do the trick.
enblethen
Nomad
Jan 12, 2015
Have you done any of the testing that I suggested earlier?
TC_Z
Explorer
Jan 12, 2015
bsinmich wrote:
Are you aware that you have to be holding the boost button down while trying to start the engine.

Yes, I know to hold it down. The switch is spring loaded and returns to the normal off position.
Effy
Explorer II
Jan 12, 2015
bsinmich wrote:
Are you aware that you have to be holding the boost button down while trying to start the engine.

X2. Technically this is a solenoid activated jumper and like jumper cables often you have to let them sit for a minute or so to get enough amps to crank (depending on how depleted the batteries are). So, hold the button for a minute and continue holding while you crank the engine. Think of it this way, holding the button links the batteries, releasing, unlinks them. Hold the button as long as you would if you had cables and were trying to jump start a car. It's an automatic jumper cable button.
bsinmich
Explorer
Jan 12, 2015
Are you aware that you have to be holding the boost button down while trying to start the engine.
ksg5000
Explorer
Jan 12, 2015
In my rig the battery isolator is a simple solenoid - they sometimes get "stuck" with age and a quick rap on the housing with a tool sometimes resolves the situation.