Deep Cycle Rating AH vs Reserve Minutes

[PaulLad]

Looking at a Die Hard deep cycle marine battery but instead of AH, its rated for 160 reserve minutes. Is there a way to convert reserve mins to AH? Thanks.

 

[Tomthumb62]

Those aren’t true deep cycle batteries, they’re a combo starting battery with a bit more storage capability than regular starting batteries. Keep looking for ones that simply list AH, not reserve.

 

[Vigilant24]

Looking at a Die Hard deep cycle marine battery but instead of AH, its rated for 160 reserve minutes. Is there a way to convert reserve mins to AH? Thanks.

There really isn't. If the battery is a true deep cycle battery, then dividing the RC by 2 would give something close to the (20 hour rate) amp hour capacity (so, they'd be 80 AH batteries). BUT, batteries that don't have true deep cycle features (esp--thicker plates) might also have a 160 RC as tested but have a lower true (20 hour rate) amp hour capacity.

Another trick to look for: Some batteries (I'm looking at you, Johnson Controls, sold by Walmart) are sold as deep cycle or marine batteries and are labelled with a, say "100 AH capacity". In the fine print in their documentation you'll see that this is tested at the 100 hour rate. The industry standard is to use a 20 hour rate. Lead acid batteries tested at the lower 100 hour rate test artificially higher than if they were tested at the (industry standard) 20 hour rate.

A battery designed for true deep cycling will be labelled with an AH capacity, and if they are honest it will be an AH capacity measured at the 20 hour rate.

I recently bought some marine "deep cycle" batteries at Rural King. They are made by Exide. Labelled as 110 AH. I am under no illusion that they are as good as true deep cycle golf cart batteries made by Trojan, Rolls, etc. If I were going to use them for daily power, I'd surely buy true deep cycle lead acid batteries (or, probably LiFePO4 batteries). But, mine are for emergency use only, and for short term use at that. I think they'll be good enough, and when they age out in 4-6 years, maybe I'll replace them with (then cheaper, better) more modern batteries.

 

[Rednecktek]

Yeah, gotta love the sticker on the WallyWorld batteries that state 122ah (@1ah)