That small solar panel is a good solution, but it may not keep up. If the chassis battery goes bad after two weeks it is discharging at 5-6 amp hours each day. That small 10 watt panel may not keep up with that.
That much current is not right. My new Axis 24.1 has a Precision Circuits BIM 160 but yours may have the older BIRD. Both are bidirectional and the coach should keep the chassis charged and visa versa. So something isn't working right both the total draw on the chassis battery and that the coach is not keeping it charged up.
See if you can borrow or even buy a clamp on ammeter. Here is a pretty good one on Amazon for $83-
https://www.amazon.com/Klein-Tools-C...%2C265&sr=8-34
With the clamp on ammeter you can measure current either directly from the battery to confirm that it is leaking 6/24 or about 0.25 amp. Then check at the BIRD or BIM terminals to see how much may be leaking there.
David
Thor Forums
