In the beginning of August after not driving the van for approximately four weeks, I went to start the van and had no power in either the start battery or the cabin battery. I thought I had activated the cabin battery disconnect the last time I had driven but perhaps this was not the case?
I jumped the start battery (per Sprinter manual instructions) and ran the engine for about 30 minutes. I then put the van on shore power overnight. In the morning, both battery systems appear to be fully charged. I drove the van over a two-week period without a problem and all appliances seemed to work fine.
On August 23, the van went into MB for service. Afterwards, I checked out all the cabin electronics to make sure everything was working.
On August 22 we drove to Seattle. About half-way over to Seattle, we stopped for lunch (in the van) and all cabin lights and appliances appeared to be working. However, we arrived in Seattle and there was no power in the cabin. I put it on shore power with no results and checked all breakers and fuses without results.
I took it into Airstream of Spokane the next week and the service department reported that the cabin batteries (lithium) had no charge and the battery management system (BPS) would not allow the batteries to be charged by any of the “passive” methods (shore power, alternator, solar or generator). Airstream service charged the lithium battery directly (placing 12V
charger directly on the battery) and after the charge everything seemed to be working.
So here is the explanation I am getting:
When the cabin battery is “disconnected” (either using the switch by the sliding door or manually disconnecting under the back seat) there is still a significant draw on the battery. This is “as designed” and it will completely draw down the cabin battery in 3-4 weeks unless the battery is augmented by one of the passive charging systems. Once the cabin battery goes below a certain level, the BPS locks out the passive systems (including shore power). The only way of charging the battery is by direct charging (i.e. getting under the van and connecting the battery charger to the lithium battery).
The service tech claims that there is no documentation or technical note from Airstream and this is the first time they have seen (or even heard of) this issue (although from our discussions I suspect that he is new to working at Airstream service). One work around he suggests is putting in a battery isolation switch that completely disconnects the battery.
Now I am an engineer who spent his life building advanced control systems and from a design viewpoint, this seems wonkey in a number of ways – both the fact that there is no software cut-off (voltage goes below X.X volts, an isolation switch is thrown) and that the BPS forces you to use direct charging. However, I admit that I rarely used lithium batteries as anything but as a UPS.
So, I have two questions for anyone who might have info on this:
Is the explanation I am getting from the tech actually legitimate?
If so, is an isolation switch a good idea?
Thanks for your help. After a year and two cross country trips to see our daughter and grandson, we find the van to be a great way to travel. But this has ne shaking my head a bit. Does no one else leave their van for 4 weeks w/o driving it or out in the sun?