[MKappeli]

Hey everyone, so couple years ago i came across a problem where my truck was draining the battery suddenly... At the time I concluded based on many other peoples testimonials as well as sitting in the car while its off that the factory head unit's cooling fan wasn't shutting off. Well i finally decided to address the issue before hitting the road for 2 months driving across the country. So a couple days ago i removed the old factory unit which i was replacing with a DynaVin unit. So i had some issues and left it alone... During this time, no head unit has been connected to the truck and i just went to fire her up and nothing. Dead to 4.5v... so plugged her in and charging now. Do any of you recall any battery drains other than above mentioned? All suggestions and advice is welcome.... This probably one of the most annoying problems. None of the amplifiers in the back are triggered on, so its not that... The one idea I have that could very well be the culprit is that I have a power bank Gel battery hooked up in parallel as per instructions that goes straight to the power distribution for the amps... This battery is extremely old and Im starting to get the feeling that maybe its what is robbing the power.

 

[AlanMcR]

The second battery is the likely cause. Think of it this way. If you parallel two batteries, you get the reliability problems of each battery. Whichever battery fails first takes the other one out with it.
Expedition vehicles will often carry two batteries, but they are isolated from each other to prevent exactly this kind of problem. Sometimes they'll go as far as installing two alternators. This I find to be overkill, most alternator problems are easily field repairable, with the exception of bearings. And, if the bearing fails, you can't spin the belt, so in that case two alternators double your risk of failure.