Battery Shopping and Capacity Confusion

[Stu Jackson]

PorFin's right.

Even with 4 or 5 Group 24 batteries in your new house bank, you'll be just fine for a weekend with a fridge running. 5 x 60 ah each = 300 ah, 50% usable, 150 ah. You could turn the fridge off at night when no one's using it.

Here's an example:

Reply #9 "Breaking In" New Wet Cell Batteries

Understanding the difference between (instantaneous) amps and amp hours is critical to understanding electrical systems, so do some reading up.

We have a Link 2000 also, and it's a great tool. As eith all tools, when used correctly...

Good luck.

[hellosailor]

You may find a 10% variation in the rating of different "Group24" or other same-size-group batteries depending on the maker. But think carefully about Optima! They are ROUND AGM cells, combined in a RECTANGULAR case. That means they lose about 10% of the possible volume in that case, so they lose 10% capacity compared to flat-plate AGM batteries in the same size group. they are also about 50% more expensive than flat-plate AGM batteries, even though spiral construction is supposed to be both stronger AND cheaper.
Optima? Not for me, no thanks, not at that price with reduced capacity to boot.

I'd also suggest measuring your battery spaces carefully, there are some slightly different sizes (like Group31) that may be an inch higher or wider or otherwise "close" that can again push your capacity 10-20% higher without getting into batteries that are too big for one person to handle.

[visi0n]

All great information, especially the books -- good stuff. Wish I had them about $1k ago

I'm aware, of course that my radar won't always be running, nor will the vhf when I'm at anchor. But, I do see those amp hours being gobbled up readily by the kids watching a dvd before bed in the event we're under storm and not on the beachside camping.

I'm basing the load conditions off of a online calculator more than observation on my link, since I'm using far more busy sailing than playing with electronics in practicality. I'm thinking the TV use at anchor is really what's pushing me past the limit. Maybe time to just bring a 4 or 5 hour portable and not chew down my boat's bank.

this calculator:
Marine & RV Battery Load Calculator

I've seriously considered these Duracell's I've seen at Sams. They are only $100, which kind of concerns me. ;/ Looks like I have some reading to do..

[visi0n]

Thanks all, for the help.. Glad I asked.

I sort of ran out of money for this project until some of my customers settle their debts, so I'm part of the way there..
Got the batteries from Sams, hopefully they'll hold up.

I put two Duracell AGM Golf Cart (200 ah) batteries in series on the house side. (I have just enough room for two more in the coming weeks, for a series/parallel wiring)

and two Duracell 12v 55ah Marine AGM's in parallel on the alternator for starting.. Why two? Well, I'm a little nervous about a failure in the series and somehow being down to a useless 6v leg, so I see the second 12v AGM as a hot-standby that could be readily re-wired or switched, at least until I can complete the houe bank in the coming weeks..

As it stands, it gives me 200 ah rated bank on the house for now and room to add two more identicals and push up to 400 in the coming weeks when I'm feeling froggy...

Thanks again for the suggestions, Sams prices were really pretty reasonable, especially compared to West Marine and the Auto parts dealers. Hopefully the reasonable price doesn't bite me.

[Stu Jackson]

Why not use one of the 12V for the reserve bank and combine the 2 6V and the other 12V. Your house bank will be bigger and better and last longer. Perhaps you're missing the points mentioned in this entire topic.

[visi0n]

The 6V serial have different capacities and charge/discharge characteristics than the 12volt.

My charger manual warns against charging disparate batteries amongst a shared bank. Even though they share chemistry commonalities, they are very different in discharge rate, etc.

The 12 volt AGMs are only 55 ah, anyway. It's a higher crank amp, lower capacity battery. I wouldn't want to risk nuking my charger, negating it's safety algorithm or grenading my batteries for a measly 55 amp hour, at this point.