Battery size requirements for starting/jamming tunes

[Homeskillet]

Sooooo.... I'm already wondering if a new battery is in order. I have 2 group 24 batteries (M24 -1010CA). As many of you already know, I have 2 amps, a sub and 6 JL's ready to rock. I do NOT think my batteries are dual purpose batteries. So I suspect they will drain pretty fast if anchored and rockin'. I feel like I should put something in there with more reserve minutes (my trolling motor batteries for my fishing boat had 205 min of reserve - not sure about cranking amps but it didn'tmatter because they were only for the TM). Hard to find 1000 cca's and a lot of min with out dipping into my kid's college fund lol!! Do I really NEED 1000 cranking amps? I have a 2005 6.2 MPI Mercruiser MX. Not a member at Sam's Club or Costco due to proximity. Any recommendations?

[Big Block Power]

This is what I have and I have pretty much the same set up. I'm not changing anything til I try it on the water.

[jhnmdahl]

Even though you may have a 600 watt amp and six speakers you feel like are pretty loud, the actual “program power” or average power drawn at normal listening levels (i.e., not cranked for the people swimming 40 feet away, no sun turned up to rattling the screws loose) is typically less than 10 watts or so. Figure maybe 75 Amp-hours out of a group 24 battery, and you can estimate how long a certain load should be able to run.

Most starting batteries fully charged can run a stereo all day - the problem is when an already-weak battery starts the boat ok at the dock, but loses just enough after cranking music all day, running a toy inflator, maybe a mini-fridge or some lights, etc., that it can’t quite start the engine when it’s time to go home.

One idea I like is to keep the “new” battery as your starting battery and the older battery as the house battery, and swap out the oldest battery every 3-4 years.


Edit: For DC sources like a car battery, P=I*E, which is power is voltage times current. Something drawing 10 watts at 12 volts will therefore draw 10/12, or .83, amps, which means that a battery with a 75 amp-hour capacity could theoretically run it for around 90 hours under ideal conditions.

[Homeskillet]

Okay thx. So I just might be alright then... I think I'll follow suit and give her a whirl before overthinking it.

[cmattj]

This is what I have and I have pretty much the same set up. I'm not changing anything til I try it on the water.

Nice.. No start date ..forever warranty ... brilliant

[akorcovelos]

Just buy a jump box and keep it on board, then when you find the weak battery use the box to crank and replace the battery when you get home. Always good to have a jump box on the boat anyway, I’ve used it on other peoples boats more than mine.

[Big Block Power]

This is what I have and I have pretty much the same set up. I'm not changing anything til I try it on the water.

Nice.. No start date ..forever warranty ... brilliant

It's warranty is until it doesn't start

[Homeskillet]

I just ordered an onboard charger from Amazon. I got a Guest (2 bank, 4 amps per bank). I know there are way better ones out there (I preferred the Dual Pro's for my trolling motor batteries). But I don't think need something of that caliber. Slow charging is better for them anyway, I think. I'm not even going to add the inlet receptacle because I don't want to saw a hole anywhere lol! I'll just hang the cord out the hatch.

[BrockA25]

I run, and have very happy with my dual Optima 31 Blue tops. One of them alone will push 2-Rockford T2 12's, powered by dual 1200 watt sub amps, along with 10- Rockford 6.5s and tower speakers, powered by 2-600 watt amps, 4 amps total. The other battery is designated for my engine. Can play loud for hours, but after about 4 to 5hrs you better have a back up plan. I also have a dual charger, and charge my batteries 24/7 365 when not on the water. Keeping them fresh and fully charged prevents sulfate build up and prevents capacity loss.
With my boating and music habits over the last 10+yrs and 3 different boats, one thing I learned is good batteries suck if you don't take care of them and charge them properly. A jump pack on board can also be your best friend someday...lol