Charging /flooded lead acid battery off of a solar panel/ sealed AGM system.

[AWS]

So not only installing an isolator I also have to reduce the amperage to 15 amps for a 70 AH battery.

[Mike90250]

Depends on the vehicle. A 35A alternator will take much longer to recharge a battery than a 120A alternator. Larger vehicles have larger alternators. Also depends on conditions, rain, night, wipers, lights siphon off some of the charge power, and it's not available to the battery.
For simple math, a 100Ah AGM battery could be safely charged at 20A. (20% of it's capacity). if the battery was half depleted, it would take 110% to replace the 50Ah consumed, so 50ah / 22 = 2.3 hours IF the alternator was set to the right voltage for charging an AGM battery.

[AWS]

The battery Isolator sounds interesting. I usually have to travel between the campgrounds and the lake and travel to hunting areas and only stay in one place for no more than 4 days. By upping my AGM house battery to 70 Ah my furnace should run a few days.

How long would it take the vehicle alternator to charge a 50% depleted 70 AH battery. Could I wire in a switch to divert the line to the house battery to charge the boat battery?

[SunEagle]

That MPPT charge controller may get confused if you used a jumper wire between your spare FLA and your AGM because it would really not know what voltage is for the battery that needs to be charge. Also like two tanks of water that are connected to each other the battery charge will balance out just like the two water tanks. So basically you will discharge your AGM into your FLA which uses up the AGM's life.

I would disconnect the AGM before I connected the spare FLA and let that 100 watt panel charge each battery individually but depending on the Ah rating of that spare FLA battery a single 100 watt panel may not perform a good charge.

You could follow Sunkings advice and use teh engine alternator to keep both batteries charged since that 100 watt panel at best has maybe 5.5 amps of charging ability for a couple of hours a day. It might be better to save your money by not purchasing the 100 watt panel and CC

[Sunking]

Why use a Solar Panel?

Get an Electronic Battery Isolator and use your engine alternator to keep the battery charged. Your engine running 15 minute generates more power than a 100 watt panel can generate in several days. A 100 wat panel mounted on a van is not going to keep that battery charged up and meet your needs.

[AWS]

I'm installing a 100 watt solar panel, MPPT controller and sealed 55 AH AGM battery in my van to run a small propane furnace (Propex 2000) in the winter and a roof fan for an hour when I go to sleep at night in the summer. Can I run a jumper cable from the AGM battery and use the solar system to charge my spare lead acid flooded boat battery when I have nothing running in the van?