Interstate Batteries
 

Trying to decide on batteries...I can get interstate free, so pretty biased to that brand. However they don't list Amp hour ratings like the all the rest of the ones I am looking at. Sooo, really have trouble comparing. I'll be running about 2500 rms and want to be able to play for several hours between chargers. Here are their two biggest ones. Not sure how this compares to something with an Amp hour rating.


Interstate Batteries SRM-29 Marine and RV Deep Cycle Battery
CCA: 675
Cranking Amps: 845
Voltage: 12
RC Min.@ 25: 210
Width: 6.75”
Length: 13.00”
Height: 10.00”
Weight: 59.30
Termination: M
Free Replacement: 12 months
Pro-rata Warranty: 30 months

Interstate Batteries SRM-4D Marine and RV Deep Cycle Battery
CCA: 1314
Cranking Amps: 1645
Voltage: 12
RC Min.@ 25: 390
Width: 8.25”
Length: 21.00”
Height: 8.25”
Weight: 116.80
Termination: M
Free Replacement: 6 months
Pro-rata Warranty: 30 months

The group 29 battery should be around 110-120 AH the SRM-4D will be around 200 or so AH.

For 2500 rms watts 3 group 29's or 2 SRM-4D.

If it wre me I would just do 3 group 29's.

I've got 4,055 watt RMS system and will be running 3 interstate 29s for my stereo bank FWIW. Is sat you'll have plenty of play time either way.

I'm pushing close to 4k watts and use a SRM-4d with a srm-29 as a back up. We use the stereo hard for the majority of the day during holidays and the 4d is awesome. Personally thats what I would go with.

Think I would have trouble draining that 4d in one day?

I was thinking of keeping a separate stereo bank disconnected from everything. Then just use a shore charger.

Just for comparison... I'm running around 2300 watts RMS on 2 Interstate SRM-24. They are separated from the rest of the boat by a Perko switch. I consistantly played 8-10 hours a day on back to back days multiple times over the last 2 seasons with no signs of power loss. I would plug in the shore charger at the end of the day and let them charge over night. These batteries are about 4 years old now. I have a separate SRM-27 that does all other boat functions besides stereo. I plan to move to SRM-27 or 29 once these 24s give out just for the extra capacity, but I don't really need it.

I ran 2 SRM-24 from 2003-2010 before one finally went bad. I replaced both at once and added the 3rd with a stereo upgrade. I know they aren't the highest amp/hour batteries around, but they have done great for me in the past and the prices are not bad.

Based on the amp/hour ratings of known and conservative group 31s, some may be over estimating the A/H rating of the Interstate 29. But in any case, it is a good battery with tons of capacity.
With Class D amplifiers your current usage will be less.
You do not want to regularly run these batteries down below 12.0 volts. So if you discover that two group 29s for example, are not sufficient, add a third immediately before there is much age on that bank.
I would not isolate the stereo bank from my boat's charging system. An infinite number of fully charged batteries do not represent a challenge to your alternator. By allowing the alternator to service the bank throught the day, and until you have a stay at rest, you are maintaining a higher voltage and greater reserves. Then if the bank is deeply discharged after a long stay at rest, you have the option of not re-introducing it to the charging system.
Your amplifiers are playing AC based music content, unlike the constant draw of a DC bulb, so the current draw will not approach simple wattage/voltage/efficiency calculations. The stereo with a charged battery bank is not going to be too much load for the alternator.
Your amplifiers are going to drop 25% of their 14.4V power rating with a more realistic 12.5V supply. And they will lose another large % of power when the voltage drops to 12.0 volts or below. So keeping that voltage high is important to the audio system power and important to the longevity of the batteries. You will get an inordinate increase in number of cycles if you avoid deeper discharges and an inordinate decrease in number of cycles with deeper discharges. It's not a linear ratio.

So after jamming all day and depleting my banks the alternator is going to start charging those at least on the ride back to the dock. Could be a couple hours if we are putzin around. Is that going to toast the alt? I don't see disconnecting the alternator from the stereo/accessory battery at that point because that combined bank of batteries runs everything but the starter on my boat. I have a battery isolator but not a perko dial switch.

I'd buy something like a D3100 from XS Power Batteries to run my stereo while floating, and switch to a basic flooded batter for cranking and general running around. Either install a charging system for the D3100 or just throw it on a charger when you get home. I've been running the same two D3100's since '10...

And my stereo's have consisted of anywhere from a syn1 and 2 syn2's to two sd2's and an sd6.