Battery set up question!!

[david.g]

I have a 23' Chapparal. I am upgrading the stereo system (replacing 4 interiors, adding 2 towers, adding 1 sub, adding 2 amps). Not a huge system but a good one. The plan is to install a secondary deep cycle battery to run the stereo for hours if at an island.

My issue is i use a dry stack so i have no power available to recharge the deep cycle when i return. I know between the starting battery and the new deep cycle, the new deep cycle isn't going to get crap for a recharge on the ride back or just riding around a little while.

Only option i can think of is removing the deep cycle after each trip and taking it home with me which sounds terrible. Someone suggested sticking with a single battery just upgrading to a good solid dual purpose. Said that i would probably never kill the dual purpose, the dual purpose would recharge faster while driving being the only battery, and i can carry a jump box just as a precaution.

Any better ideas?

Thanks!

 

[Scott Danforth]

they make battery switches just for adding and isolating batteries.

I suggest a 1/2/both switch and an ACR (automatic charge relay) for the house battery. that way you charge the battery as you boat along. plenty of threads on adding an ACR. just use the search function.

BTW, with all that stereo, you will need to add two extra batteries. amps kill batterys fast.

 

[dingbat]

Someone suggested sticking with a single battery just upgrading to a good solid dual purpose. Said that i would probably never kill the dual purpose, the dual purpose would recharge faster while driving being the only battery, and i can carry a jump box just as a precaution.

Any better ideas?

Thanks!

A dual purpose battery buys you nothing. A glorified starting battery at marine pricing. If you want an “upgraded” battery you go to AGM

Couple of questions that need answered:
1. What is the total current draw (amp/hrs) of the stereo system in question?
2. What is the boat’s charging system rated for?
3. How long do you run the boat each time out?

Gut feeling is that you might be able to get away with a large deep cycle (grp. 27 or 32) but charging is always the issue.

As Scott noted, automatic charge relays (ACR) work well in this application. Problem being you need to run the boat. Ten minutes up and back to the sand bar isn’t going to cut it. Battery life will suffer unless the batteries are fully recharged after use.

 

[KD4UPL]

Why do you think the deep cycle won't be charged by the engine when you are running around in the boat? Is it a real short trip to the sand bar? I assume you have an I/O set up with some kind of V8 engine. It should have a decent alternator, if not you can always put on a bigger one.
If, for instance, you have a 100 Ah deep cycle battery and you drain it down 50% with the stereo you need to put back in 50 Ah. Most any alternator should be able to deliver 25 amps to the battery when running, likely double that. So, with only 3 hours of engine operation the battery would be fully charged; likely less. Do you not run the engine that much?
On my boat I have 3 amps driving 6 speakers and a sub woofer. I keep it on pretty much all day. I probably put run the engine a total of 3 or so hours during a 6 to 8 hour lake outing. My batteries stay charged up pretty nice. I don't know the size of my alternator but it's the factory one on a 2004 Mercruiser Mag 350.

 

[H20Rat]

BTW, with all that stereo, you will need to add two extra batteries. amps kill batterys fast.

Not to disagree, but... 2 amps, 1 sub, couple of main speakers isn't big, and is going to run just fine on a dedicated battery. 2 batteries for that is massive overkill unless he needs it running all day long without the engine on. My current system is substantially larger and I have a single large battery for the entire boat! (I competed and won regionally in IASCA sound competitions back in the day, I've also entered and won a competition for cars, with a boat! That particular boat had 3 batteries, 5 amps, 4 12" subs, somewhere around 20 speakers)


For the OP, it all depends on how much key-off time you expect and how loud you run it. On my current system, I'm running 2 large Skar amps, a beast of a skar sub, and 6 mains. All powered off a group 31 deep cycle, which also starts the engine just fine. I've had run times at decent volume up to about an hour and still started the engine without issue.

 

[Scott Danforth]

a single battery wont cut sitting on a sand bar for 3-4 hours. the one hour you mention, no problem. however since the OP states he wants to be there for hours in post #1...... I take that as a minimum of 3-4 hours. a single battery would be dead. that is simple math using current draw and discharge rates.

 

[david.g]

Thanks. I am going to go ahead and do the dual battery with ACR just to be safe and as a back up in case a battery fails. My boat has a 5.0 in it. After thinking about it, if I am out for the day (7-8hrs) it will probably be split half and half between driving and being stopped at an island with the stereo on so the more i think about it i should have no issues on getting recharged.