Dual Battery Setup?

[jgruberman]

I've been considering adding some better speakers and radio and maybe even a marine amplifier for those speakers, then came the topic of "Well I should add another battery to be safe". So my question is... how are people adding second batteries with limited space? Picture included in link, so not sure how to proceed with this.

https://imgur.com/a/nZcJCdB

[belercous]

You simply add another battery wired in parallel to your existing one. If you want to have a decent (clearly audible) stereo system you should have a second battery. I run two batteries (I'm not near my boat so I can't tell you the brand) of batteries which are a cross between a starting & deep cycle battery. Starting batteries are meant to put out a lot of amperage for a short time, while deep cycle batteries are meant to be used for a constant draw such as trolling, or powering a decent sound system. "Decent" starts at 50w RMS @ 8 ohms per channel. I run a true 175w system. Bass eats up a lot of power.

I run a pair of Klipsch indoor/outdoor spkrs. Kilpsch spkrs are noted for being efficient so they put out a bit more sound for the input power. When buying a stereo, be wary of the power rating. An amplifier which is might be rated at 200w might actually only produce 50w. What manufacturers often do is rate their amp's output in 4 ohms instead of 8. Those amps only produce 100w in 8 ohm spkrs if they rate the amp at peak power instead of RMS. (See how they just doubled the power of their amp, as compared to a home stereo? Well they often double the output again by adding the power of both channels, so now that 200w amp is only putting out 50w when compared to a home stereo. My true 175w (into 8 ohms, per channel) amp could be advertised as producing 700w. Car stereos are often rated this way to make them seem more powerful than they are.

To match spkrs to an amp, first figure out what the amp actually produces, RMS, per channel, then get a pair of spkrs which are rated close to that at the same rated impedance. If the spkrs are rated for more wattage, they'll last longer but won't be as loud as ones rated at a lower rating which will be louder, but may not last as long under constant full power. Matched spkr/amp systems will work fine all day long under full power. Unless you're cranking at max volume for 30 minutes or more at a time you can get by with spkrs rated 25% less than the amp produces. What kills amps & spkrs is overheating, which comes from being used beyond their ratings. (On a spkr that means pumping in more power. On an amp that means reducing the rated impedance of the spkrs.)

My stereo & amp are automotive & have lasted years for me. Marine grade might be better (longevity-wise), but as my boat isn't in salt water I didn't feel the need to spend the extra bucks for marine grade.

[Moser]

I'd turn that battery 90 degrees and put a second battery right next to it. Move the wires for the house stuff to the new battery and leave only engine and maybe factory lights to the starting battery. I would go with whatever group 27 or 29 deep cycle is on sale and put a Yandina batterty combiner between the starting and house batteries to keep both topped off, and isolate the starting battery from the house battery when you are cranking the tunes. The combiner will allow the engine to charge the house battery once the starting battery is at 13.5 volts, and it will disconnect the 2 batteries from each other, when the combined voltage falls below the 13.5 mark. Get a box for a group 31 and put something in the end (block of 2X6 wood, or piece of PVC pipe) just to keep the smaller battery from sliding around and you can put the combiner and wires on top of that, in the box with the new battery.

[jgruberman]

You simply add another battery wired in parallel to your existing one. If you want to have a decent (clearly audible) stereo system you should have a second battery. I run two batteries (I'm not near my boat so I can't tell you the brand) of batteries which are a cross between a starting & deep cycle battery. Starting batteries are meant to put out a lot of amperage for a short time, while deep cycle batteries are meant to be used for a constant draw such as trolling, or powering a decent sound system. "Decent" starts at 50w RMS @ 8 ohms per channel. I run a true 175w system. Bass eats up a lot of power.

I run a pair of Klipsch indoor/outdoor spkrs. Kilpsch spkrs are noted for being efficient so they put out a bit more sound for the input power. When buying a stereo, be wary of the power rating. An amplifier which is might be rated at 200w might actually only produce 50w. What manufacturers often do is rate their amp's output in 4 ohms instead of 8. Those amps only produce 100w in 8 ohm spkrs if they rate the amp at peak power instead of RMS. (See how they just doubled the power of their amp, as compared to a home stereo? Well they often double the output again by adding the power of both channels, so now that 200w amp is only putting out 50w when compared to a home stereo. My true 175w (into 8 ohms, per channel) amp could be advertised as producing 700w. Car stereos are often rated this way to make them seem more powerful than they are.

To match spkrs to an amp, first figure out what the amp actually produces, RMS, per channel, then get a pair of spkrs which are rated close to that at the same rated impedance. If the spkrs are rated for more wattage, they'll last longer but won't be as loud as ones rated at a lower rating which will be louder, but may not last as long under constant full power. Matched spkr/amp systems will work fine all day long under full power. Unless you're cranking at max volume for 30 minutes or more at a time you can get by with spkrs rated 25% less than the amp produces. What kills amps & spkrs is overheating, which comes from being used beyond their ratings. (On a spkr that means pumping in more power. On an amp that means reducing the rated impedance of the spkrs.)

My stereo & amp are automotive & have lasted years for me. Marine grade might be better (longevity-wise), but as my boat isn't in salt water I didn't feel the need to spend the extra bucks for marine grade.

My question was specifically about fitting the battery housing. I own a car audio company, so the issue isn't HOW do I add speakers and an amp, specifically how I produce the room for the second battery. @moser Got me the answer I was looking for, thank you!

[jgruberman]

I'd turn that battery 90 degrees and put a second battery right next to it. Move the wires for the house stuff to the new battery and leave only engine and maybe factory lights to the starting battery. I would go with whatever group 27 or 29 deep cycle is on sale and put a Yandina batterty combiner between the starting and house batteries to keep both topped off, and isolate the starting battery from the house battery when you are cranking the tunes. The combiner will allow the engine to charge the house battery once the starting battery is at 13.5 volts, and it will disconnect the 2 batteries from each other, when the combined voltage falls below the 13.5 mark. Get a box for a group 31 and put something in the end (block of 2X6 wood, or piece of PVC pipe) just to keep the smaller battery from sliding around and you can put the combiner and wires on top of that, in the box with the new battery.

What do you mean by "house" battery? Current I have a spare Duralast Blue Top(24MD-DL) I was going to use but if I need a different size battery for fitment then I can do that also.

[rickdb1]

The house battery would be the one that powers the radio, amp and speakers. Isolated from the starting battery, which would be solely used for starting the engine and powering the running lights.. The "House Battery" should be a deep cycle type battery.

[Moser]

I am certain he appreciates the time and and effort you put into your response though, Belercous. The Duralast looks like a deep cycle, so it should do the job, the group numbers I referred to designate a size for the battery, 27 and 29 being the most widely used for deep cycle, your 24 should be fine. I'm sure you can do the math to decide if it has the capacity to power your system and know just how long you can push it, and just how hard, before it runs out of reserve.