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Amp hours vs reserve capacity

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Always tossed batteries into my boats based on CCA. Put batteries in forklifts according to Amp hours. Duh, when I tried matching up a couple batteries to run a redi-line generator it dawned on me cold cranking amps don't mean a damned thing to a deep cycle battery. Reserve capacity (minutes of draw @ 25amp) will tell you a lot more about what a battery can provide over time, along with Ah (amount of hours a battery can provide a 1 amp draw). Was charging some deep cycles I had laying around, that had run trolling motors well (in series, as well as by themselves) and I noticed one battery was pulling a lot of amperage off the charger. Exide 1000cca, but only has 115 minutes of reserve. Damn, that thing won't provide enough wattage to run a Redi for an hour. A  690cca w/101 AH has double the capacity. Live & learn, that's why I'm an idiot.

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For sure they rate deep cycle in minutes at 25 amps , but every battery has a different curve of discharge time at lets say 4 amps.

i think you can find charts of your kind of battery to compare .

but also there is different type of deep cycling some use for VR need longer power reserve and somme they have the crank power to start engine.

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Things I have learned (often the hard way) about batteries in recent years

Lithium batteries are killed by the cold, don't buy for your vehicles if you live in cold climates

A good make lead acid battery should last 8-10 years, gel batteries only last 2-3 years in normal use

Batteries that need to be constantly recharged (deep cycle) again only last 2-3 years in normal use, there is a limit to the amount of recharges they will take. I am currently experimenting with carbon gel batteries (not cheap) more power, more charges, and I hope for at least 5 years.

Batteries are damaged if constantly run down to less than 50% before recharging ( electric cars ???) lead acid sulphate and deep cycle lose charging capacity.

Deep cycle do not achieve full capacity until after a few charges.

Gel are better for most purposes than AGM

I have now installed voltmeters (rather than ammeters) on electric battery machine 'draws' as this gives the best indication on when you are running into trouble, provided you research your type of battery.

Batteries are a complex subject, do your research before buying, your average car battery is not good for some purposes.


Lithium batteries once fully discharged cannot be recovered (at least with present tech), they need a special charger too.

Lead acid (and to some degree AGM/Gel) if fully discharged and sulphated it may be possible with a smart charger to recover, but their life will suffer compared to a well maintained battery.

If you don't use batteries regularly (motorcycles, jet skis etc) invest in a smart charger that will maintain the battery, especially in cold climates.

Cold is the enemy of every battery currently in normal use.

Edited by RobMc
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