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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #1
During winter storage of my class b motorhome (promaster 3500 chassis) I disconnect my starter AGM battery and then reconnect it every couple weeks to drive it. If I leave my battery connected it has dropped from 12.7 to 12.0 in a little over a week so I disconnect it.

I always check the battery voltage before reconnection and it usually is 12.7. After reconnecting the negative cable again, I wait about 10-15 minutes before trying to start it, with all door closed, no lights, etc. Most of the time it will start up but occasionally it won't crank when I turn the key and I may have to try multiple times before it will crank and dash indicators come on. I've even had it to where I can't remove the key after failing to start unless I disconnect the negative battery cable letting it sit awhile and then reconnecting the negative battery cable which then seems to release the key.

Thoughts on what is going on and how to fix it??
 

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MMXVI - L2H2 in IN
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Make sure you have a clean connection between the post and clamp, and make sure you seat the clamp all the way down on the post.

and while you are at it verify the pos clamp is all the way down.

Something in your van is drawing power, the van should easily do 30 days with minimal loss.
 

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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #3
Make sure you have a clean connection between the post and clamp, and make sure you seat the clamp all the way down on the post.

and while you are at it verify the pos clamp is all the way down.

Something in your van is drawing power, the van should easily do 30 days with minimal loss.
Thanks for the reply Phil.
I'll try and make sure regarding your suggestions.

I did a multimeter reading for parasitic draw by disconnecting my negative battery and using the probes on the negative post and negative cable. I had a reading of mostly 10-20mAmps with an occasional jump to 70-80mAmps but that might have been due to my shaky hands causing minute loss than recontact of point probes.
 

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2019 Ram Promaster 136 HT Gasser Stealth Work Van Weekend Camper
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@phil said ...A fully charged battery will not crank if terminals are not seated correctly on post .
 

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2021 3500 Extended
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Every 'motorhome' I have had all came with a nice factory installed parasitic draw that would kill the battery in less than two weeks. One did not even have the capability to trickle charge the engine battery when hooked up to shore power so I had to add that myself.

OP, Instead of disconnecting and reconnecting at the battery, consider installing a battery cut off switch which are common in marine applications:
BLUE SEA SYSTEMS m-Series Mini Single Circuit ON/OFF Battery Switch with Removable Knob | West Marine
 

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MMXVI - L2H2 in IN
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for ref this is my van, others might be different
71663
 

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Does it still have the original battery? Have you load tested it?

FWIW, during the early days of our build, the van sat for 3+ months without being driven. After that, it barely started, but it did start. That's when I hardwired a smart trickle charger that gets connected to shore power when it's parked at home for extended periods. The battery still acts new.

BTW, the factory starter battery in our 2017 gasser is a no-maintenance flooded. Diesels came with AGMs.
 

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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #8
Does it still have the original battery? Have you load tested it?

FWIW, during the early days of our build, the van sat for 3+ months without being driven. After that, it barely started, but it did start. That's when I hardwired a smart trickle charger that gets connected to shore power when it's parked at home for extended periods. The battery still acts new.

BTW, the factory starter battery in our 2017 gasser is a no-maintenance flooded. Diesels came with AGMs.
The battery is a new replacement AGM battery for a no-maintenance flood battery that has been load tested.

I have to keep the van/Motorhome in a RV covered storage area that doesn't have any ac available. Since the storage is well covered and in Oregon I'm not sure a solar trickle charger would work.
 

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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #10
double check the plus side, I had similar experience and that was the problem.
When you say check the plus, are you talking the connection to the positive post by clamp or the fuses sitting on top of the positive battery side??
 

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It is the post attachment, it was so loose I lifted it off but would intermittently start. If it is loose make sure to check it for carbon/corrosion and sand/brush to bare metal.
 

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The telltale is the key capture. If you were to disco the battery, insert the key and turn, obviously nothing would happen but it would mechanically capture the key. There is a physical bypass for this, but that’s what it does.
Mine will be hesistant to crank on the first turn after i disco the battery. I assume it’s a computer rebooting issue. Turn and hold, and it starts.
 

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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #13
for ref this is my van, others might be different
View attachment 71663
I was wondering if it is harder on the promaster to frequently disconnect the battery in order to keep battery at close to fully charged or to leave it connected and go drive it for 30 minutes whenever that battery voltage drops to 12.2 or so ??? Adding some sort of trickle charger (solar or outlet ac) is not an option.
 

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2017 Promaster 3500, 3.6L, Gas, AT, 159WB, HR Class B Motorhome
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Discussion Starter #14
Every 'motorhome' I have had all came with a nice factory installed parasitic draw that would kill the battery in less than two weeks. One did not even have the capability to trickle charge the engine battery when hooked up to shore power so I had to add that myself.

OP, Instead of disconnecting and reconnecting at the battery, consider installing a battery cut off switch which are common in marine applications:
BLUE SEA SYSTEMS m-Series Mini Single Circuit ON/OFF Battery Switch with Removable Knob | West Marine
for ref this is my van, others might be different
View attachment 71663
Phil,

Any idea why the battery voltage doesn't drop a consistent amount each day if van is just sitting in same spot, without being started, and you use the same process to check the battery voltage??

I cleaned and tightened battery connections and started measuring daily voltage.

one day I lost .06v then another day I lost .01v??
 

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2021 3500 Extended
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That's bizarre....Gremlins?


You are right, most parasitic draws are consistent. Maybe temps play a role?
 

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MMXVI - L2H2 in IN
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Phil,

Any idea why the battery voltage doesn't drop a consistent amount each day if van is just sitting in same spot, without being started, and you use the same process to check the battery voltage??

I cleaned and tightened battery connections and started measuring daily voltage.

one day I lost .06v then another day I lost .01v??
Most of the time I left the meter on so I could read it without opening the doors. If you leave the van alone the electronics stayed in the same state day after day, if you unlock & open the door then close and relock it took about IIRC 15 mins or so for the meter to calm down.

I have no idea why the voltage isn't constant, probably something to do with the battery
 

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Every time you open/close a door, a vent door opens automatically inside the HVAC system, then closes itself a little while later. You can actually hear that gremlin when it's quiet.
 

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MMXVI - L2H2 in IN
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Every time you open/close a door, a vent door opens automatically inside the HVAC system, then closes itself a little while later. You can actually hear that gremlin when it's quiet.
On mine that noise is the fresh or recirc door moving, if you remove the cabin filter you can see it.
 

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MMXVI - L2H2 in IN
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Now I remember, I was worry that the meter battery would die so I reconnected the meter to the jumper terminals under the hood and didn't close the hood all the way.
 
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