Batteries and amp hours?

[Steve]

Hey everyone!

I just installed two new monster batteries on my Mac. I'm wondering if there is a formula to figure out the amp hours per battery. Here are the batteries specifics: 875 marine cranking amps/675 cold cranking amps.

Thanks!
Steve

[mike]

Steve,

The manufacturer/dealer didn't have more info on the batteries' specs? I don't know if you can figure out AH from CCA or MCA... are these deep cycle batteries? What physical size? AGM/Gel/Flooded? What brand?

--Mike

[Steve]

Yes, these are both marine deep cycle. Physical size, about the same width as a car battery, but about 1/4 longer, and 1/4 deeper. Pretty big. Bought them at WalMart, they are Everstart Maxx Marine batteries.

Steve

[Steve]

Found this through Google:

Are these specs good?

Maxx Marine Part # MAXX-29

875 Cranking Amps
205 Minutes Reserve Capacity
125 Amp Hour Rating
High performance all-purpose marine
Faster full recharge ability
675 Cold Cranking Amps
Overall dimensions: (LxWxH)
13-1/8" x 6-3/4" x 9-1/8"

Is it pretty easy to figure out how many hours a device, such as a laptop, or port. tv, will run given this many amp hours?

Thanks again,

Steve

[mike]

Are these specs good?

Sounds good to me... these batteries are just a little bit larger than my Group 31 AGMs, but mine are 100ah.

Is it pretty easy to figure out how many hours a device, such as a laptop, or port. tv, will run given this many amp hours?

Very easy, assuming the devices will run off of DC (if you're using an inverter to provide AC, I think it gets a little more complicated).

Suppose you have light that draws 2 amps. In one hour, you'll consume 2ah. So, theoretically, you could run this light for about 62 hours on one of your batteries. However, because it is strongly recommended that you not deeply discharge these batteries, they say you should only discharge them to about 50%. So, your 125ah batteries are effectively just 62ah (usable) each.

It's fairly easy to create a spreadsheet for creating a "budget" of projected power usage within a given time period... enter each device, its amp draw, and estimated time that it will be used. Multiply amps x time for each, then sum that column for total usage.

Also, if you don't already have one, consider buying a battery monitor such as the Link 10 (if your batteries will be tied together as one large bank), or the Link 20 (if they'll kept separate, with a switch to use each as needed). It is literally the closest thing you can buy to a "fuel gauge" for your batteries. One great feature is that you can set it to consider the 50% discharge level to be "empty" when calculating time remaining and displaying battery status via the LED bar graph. So, when the battery monitor tells you the battery is depleted, it's really only halfway discharged (which is what you should consider empty anyway).

Once you have one of these, you can also use to more precisely figure out what each of your devices draws.

--Mike

[Paul S]

I think it is more important to ensure that your alternator can charge them in a reasonable amount of time. Also I think it is more important to have a well built battery over one that has higher specs. Not that those are bad batteries. They should be more than fine. I have had everstarts in my cars without issue.

I went with Rolls. 2 @group 27, 112ah,190 RC, 600CCA, weighs 60 lbs each, with a 4 year warranty. At $159 each, not cheap either. It is not unusual to get 500-900 cycles out of these puppies if properly cared for.


Paul

[Duane Dunn, Allegro]

At 125 amp hours they sound like group 31 batteries, 24 is the smallest, then 27 then 31. The really big boys are the 4D abd 8D batteries. The biggest 8D's will give you 245amp hours. You obviously want as many amp hours as you can get, but even more important is the construction. A multi or dual purpose, sometimes called starting/deep cycle battery is not as good as a true deep cycle battery. (A true deep cycle is however just as good for starting.) A true deep cycle has heavier plates, more sump room at the bottom, and typically a higher content of antimony in the lead grids.

You don't get more power from a true deep cycle, but you get more longevity. They can tolerate many more deep discharges throughout their life than a normal starting style battery. A normal starting battery will last through very few 50%+ discharges while a true deep cycle will tolerate many hundreds of deep discharges.

The dual purpose / multipurpose ones are in the middle as far as construction and price goes.

[Tom Root]

AGM- Without a doubt, spiral wound, and AGM cells are the cleanest for boat use......But spec out that Rolls battery!

Those of you the know the Solar industry, know that this truly is the Rolls Royce of the deep cycle realm! Owners give glowing reports of over 20 years, and thousands of cycles for some of their batteries. But I highly reccomend semi- sealing these, and any other wet cell battery aboard in a separate plastic battery box. Simply because of an acid spill getting contaminated with any bilge water as it leans etc. It still needs to vent, and have never seen a case of hydrogen concentrations being an explosive hazard. I have seen thermal runaway, whereas the plates explode and may cause fires. This is normally when you charge a battery very quickly with too many amps.

Batteries of any type will last much longer if you charge them slowly with as few amps as you can, I have a 5 watt solar panel with a regulator I use as a maintenance charge between usage! Sears hated me years ago, when they had that lifetime warranty in the 70's. I had a vehicle for 20 years, and every 3 or 4 years, I'd go back with my proof of purchase, and get a new battery! I think I should have kept the truck, a wee bit longer, and they possibly would have paid me to get rid of it!