Battery in trunk. Ground to battery?
 

It seems I'm having some trouble finding a good ground, which may already have cost me an amp. Since my battery is in the trunk, should I ground the amp to the battery? Any danger in doing this?

according to the diagram that kinetik gives on their site in the power cell user manual grounding to the second battery is fine. i mean a ground is a ground right? thats was the document i was referred to when i brought up putting in a second battery, so i don't see any danger in doing it...but just to be safe wait and see if any of the more experienced guys answer. but if you're going to listen to me, i say its fine. if not pull up the carpet and ground to the floor, i hear thats a good spot

Take off the hinge at your rear seatbelts and grind it down smooth and use them. Thats what I did and it works just fine and i'm using a kinetik

Not to raid your thread or anything, but can you just use any battery in the back besides a deep cycle? If it's all installed correctly can any battery be used? I have a fairly good battery with about 500 CCA and my main battery with sometihng close to 875 CA. If I use a solenoid and connect the too, and just make sure the second battery stays well charged it should be alright shouldn't it?

I'm grounded to directly to the battery, and a few people have told me that's why I have alternator whine in my system. It seems it's better to ground somewhere other than directly to the battery.

see, told you it would be a good idea to wait

I ground mine to the top of the strut towers..I ground everything to the same location to help avoid ground loops.

That's what I'll be using from now on.

No danger in doing this and you should get your positive source from the trunk battery too if you haven't already. To prevent alternator whine you will want to make sure the trunk battery is well connected to the charging system. There is also a procedure for upgrading the factory ground connections that you should consider, commonly refered to as "doing the big three". Its purpose is to ensure that all system grounds remain at the same relative potential (voltage). With solid power and ground connections you will be good for future expansion. Fuse the power wire at the battery end (or at both ends if you still have a battery under the hood).

Just to be thorough, what kind of car is this? What have you modified so far? What equipment is installed?

You can do this but why the solenoid? Research battery isolators, they might suit your needs better than a solenoid. I recommend a battery box vented outside the car if you are installing a lead acid battery in the trunk.