I have a duel battery setup. A few times my main battery draws down in about 2 days and when I switch on the solenid to kick in the spare battery I get about 15 seconds of starting and it blows the 100 Amp. fuse... hummmmmmm.....
Also, Brand new starter and new alt.. go figure...

 

I tried to provide some info in your earlier post.
Now I just learned about your dual battery set up Did this problem of blowing the fuse begin after you connected/ installed the second battery?
Wondering about what provisions you have for charging that second battery and .where you have certain cables connected. A starter will draw over 150 amps and the question is how and where do you have the wiring connected.
If you took the entire second battery set up out of the system, do you still have the dead battery problem?

 

Yes, That's why I put the second battery in. I have one battery going through a solenoid that I can switch on when the main batt is dead but when it starts the solenoid stays engaged to charge both batteries. No problem with the solenoid or wiring.. tested everything. draw is 20 amps. from the starter while starting...

 

There is something amiss here and Because I don't know how you connected the wires/cables the starter should draw over 125 amps when starting. Evidently you have something connected in parallel to show such a low current reading when starting.

I can understand your reasoning for wanting to have a back-up for when the normal battery goes dead, but if we correct the original problem (drain) you should not need the second battery.

You can't do the voltage drop tests on the fuses with anything on like dome light,or anything that would be using power or it will give you false info.
I will try to assist you in determining the cause of the drain and using your meter to pin it down. To help make some of this easier consider watching some of the videos of the voltage drop procedures for ," Locating Parasitic drains". I.m sure they will shed some light on a few time saving steps.

 

I watched quite a few on para draining and it put some light on the subject too ,, thanks for the info. The main reason for the other battery is Ihave to put a printer and computer into the truck for my business. I have a invert-er to take care of that and have it hooked to the spare battery. I will check for the para drain a little later on.. and will keep yas posted.. thanks for all your help too...