Battery Capacity

[richard5933]

The Interstate batteries linked to show a reserve capacity of 390 @ 25 amps. Reserve capacity seems to be usually listed in minutes @ a stated draw rate. That's not the same thing as the Ah capacity, which is usually measured at the 20-hour mark. I'm guessing that these would have somewhere around 240 Ah @ 20 hours.

With the dual purpose batteries (marine batteries or any battery meant for both starting and deep cycle use) you usually get a compromise on both purposes. The true deep cycle batteries usually provide much more in the way of capacity and the ability to draw down without damage.

As stated earlier, it's all about the lead.

[chessie4905]

I believe true deep cycle batteries aren't rated in ampere hours. More like minutes at a specific amp draw.

[richard5933]

This was taken from: https://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80°F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an amp rating taken for 20 hours. What this means for a 100 AH rated battery is this: Draw from the battery for 20 hours, and it will provide a total of 100 amp hours. That translates to about 5 amps an hour. (5 x 20 = 100). However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 amp hours.

I've used the amp hour rating when comparing deep cycle batteries. Seems to be the standard rating for them. Since none of us are going to purposefully discharge a battery to 10.5v the reserve capacity didn't seem as valuable.

[bevans6]

The interstate 4D's linked are start batteries, not deep cycle, so as mentioned they usually don't have an amp hour rating.  A mixed use marine battery might or might not have both start and ah ratings.  The reason the 6V golf cart batteries are regarded as better for RV house use is they are optimized for deep cycle use, not start use.  As mentioned, it's all about the lead, and the way the lead is built into plates.  Weight is not the only factor, although it's a good indication of how much battery you are getting.  4D's are certainly available in both start and deep cycle, and are a favored size for a lot of marine use, my buddy has them in his sailboat.  I just bought 4 6V golf cart batteries for a great price from Costco, 25% less than anywhere else, 225 AH, for a 225 AH 24 volt house bank.  A lot of manufacturers will list the AH rating for deep cycle batteries in a variety of discharge rates, from 1 hour to 100 hours, and will list predicted charge cycle life expectancies for each.  The rule of thumb for lead acid batteries is don't discharge them past 50%, but if you only discharge to 80% you can really extend the life of the battery.  It's like "buy it, but don't use it, and it will live forever..."

[Fred Mc]

As a fellow Canadian  AND costco member Id be interested in what battery you got and the price.

Regards

Fred

[neoneddy]

Why use 6v instead of 12v?  Well I'd use 2v if I could find them reasonably priced.  2 Reasons:

• Easier to move per battery.  I'd Rather have many small parts vs one large  (heavy) part
• Less cells to possibly go bad.  a 12v battery has 6 cells, each 2v.  A 6v battery has 3 at 2v.  So if a 6v battery goes or a cell in it goes, I replace the single battery vs the whole 12v battery.

I'm buying the GC115 , a relabeled Deka Battery https://www.batteriesplus.com/productdetails/sligc115  I've told the story a few times, but here it is again.  In my store, if I ask for the on-line discount in-store, they'll sell me the battery for about $100 each.  I buy 4 at a time.  It's really hard to beat it.   I'm aiming to leverage Peukets Law and make my bank larger to try and get my amp draw below the 20 hr rate, this will increase my realized capacity as well.

[chessie4905]

 😱

[bevans6]

As a fellow Canadian  AND costco member Id be interested in what battery you got and the price.

Regards

Fred

They only have one 6V battery, this one, and I paid $140-ish, forget the exact price.  https://www.costco.ca/Automotive%2C-Marine%2C-Lawn-%2526-Garden%2C-and-Golf-Cart-Batteries.product.100017095.html

You have to call the store near you to see if they have any.  I went to two stores to get my four.