Second Battery 101

[Cj the newbie 6]

I feel like this question has been asked, but I did scour the web and went 30 pages into this forum looking for advice. But I still have questions!

When installing a second battery, some say get the same as what's under your hood, but some say it doesn't matter. Opinions?

How do you suggest securing it in a trunk?

For a battery such as an xs, do I need to put it in some sort of case?

If the batteries are wired in parallel, do I need to hook up my speakers and sub to the second or can I just leave them on the front and the rear battery will flow through it?

These are just a few examples of questions because I am completely blind and when it comes to power supply I really do not want anything not done right, but any input small or large would be appreciated!

[Billy Jack 145]

Yes you need the same size battery's or the weaker one will drain the stronger battery. And I always hook up my amps to the battery in the trunk that way you have shorter runs of wire for maximum power. And you always want to have it secured or other wise it could make contact with some metal and catch fire. Myself I ran one hot wire from my front battery to the rear and grounded my 2nd battery in the trunk with the same grounding point as my amp. But I also ran 2 grounds for my amp as JL recommended. Now my 2 battery's aren't identical but they are they are very similar in size and I haven't had the first problem. You also want to fuse both ends of your hot wire and also have a fuse between your rear battery and your amp other wise you could short out and have a real problem on your hand. 

[Randal Johnson 544]

You mentioned XS batteries in your post, which tells me you know something about this topic.

My suggestion would be to contact them and discuss this to get an idea that will work for your application.

[Randal Johnson 544]

Double post.

Edited May 31, 2016 by Randal Johnson
Double post.

[hdrox88 142]

3 hours ago, Billy Jack said:

Yes you need the same size battery's or the weaker one will drain the stronger battery. 

This isn't quite right. Just having different sized batteries connected will not cause one to drain the other. Now if one of those batteries is really old/weak, regardless of size, it may bring the resting voltage of the newer/stronger battery down to its level. Also, having mixed chemistry batteries connected can have a similar effect. Meaning, if you had a flooded lead battery and an agm battery connected it wouldn't be ideal. I've personally done that one for a short period of time(less than a year) and noticed no major ill effects, though the agm would rest at the same lower voltage of the flooded battery when connected. After disconnecting the two, the agm bounced back to where it was before.

Keep power and ground runs to the amps short as possible and make sure both connections are solid. 

[Cj the newbie 6]

12 hours ago, Randal Johnson said:

You mentioned XS batteries in your post, which tells me you know something about this topic.

My suggestion would be to contact them and discuss this to get an idea that will work for your application.

More of just hearing a reputation. I know about batteries, just not necessarily the how to's etc. But thank you I'll try that!

[Cj the newbie 6]

9 hours ago, hdrox88 said:

This isn't quite right. Just having different sized batteries connected will not cause one to drain the other. Now if one of those batteries is really old/weak, regardless of size, it may bring the resting voltage of the newer/stronger battery down to its level. Also, having mixed chemistry batteries connected can have a similar effect. Meaning, if you had a flooded lead battery and an agm battery connected it wouldn't be ideal. I've personally done that one for a short period of time(less than a year) and noticed no major ill effects, though the agm would rest at the same lower voltage of the flooded battery when connected. After disconnecting the two, the agm bounced back to where it was before.

Keep power and ground runs to the amps short as possible and make sure both connections are solid. 

The only reason I'm asking is because I can't fit that large of a battery underhood and no skills to make something to help, so I just wanted to put a little bit larger of a battery in the back! Thank you for the help!

[Cj the newbie 6]

12 hours ago, Billy Jack said:

Yes you need the same size battery's or the weaker one will drain the stronger battery. And I always hook up my amps to the battery in the trunk that way you have shorter runs of wire for maximum power. And you always want to have it secured or other wise it could make contact with some metal and catch fire. Myself I ran one hot wire from my front battery to the rear and grounded my 2nd battery in the trunk with the same grounding point as my amp. But I also ran 2 grounds for my amp as JL recommended. Now my 2 battery's aren't identical but they are they are very similar in size and I haven't had the first problem. You also want to fuse both ends of your hot wire and also have a fuse between your rear battery and your amp other wise you could short out and have a real problem on your hand. 

Thanks as always man! One more question...a battery such as an xs, would I have to get some sort of box to surround it, and also how do you secure yours in place?

[///M5 2,833]

As with anything it depends on your goals.  I have 3 pieces of crap in my boat, does more than I need.  Conveniently marine stores and craptons of websites have battery tie downs as well.  Sealed batteries don't require a case, but my non-sealed ones do.  Got the battery case from the same place

[Cj the newbie 6]

1 hour ago, ///M5 said:

As with anything it depends on your goals.  I have 3 pieces of crap in my boat, does more than I need.  Conveniently marine stores and craptons of websites have battery tie downs as well.  Sealed batteries don't require a case, but my non-sealed ones do.  Got the battery case from the same place

Thank you very much!