Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
|Author||Topic: Battery Types|
posted 04-13-2011 02:24 PM ET (US)
One thing I have not heard talked about too much is the concept and difference between deep-cycle batteries and starting batteries. Here's what I think I know: deep-cycle batteries are made to tolerate being charged and run down again repeatedly, and starting or storage batteries are NOT made to be charged and run down again, repeatedly; too many discharges and they are toast. And often it does not take many. Starting batteries are meant to be kept charged. So, why would people not just go ahead and use a deep-cycle battery for all things, all the time?
Deep-cycle batteries are bigger and heavier than starting batteries for a given cranking power. A huge deep-cycle battery will still have a depressingly weak CCA for starting, and you see starting batteries half the size, with more cranking amps. Deep-cycle batteries are expensive and wasteful, if you only use the battery for starting and keep it charged anyway. You don't use a deep cycle battery in your car--most of us don't, anyway. Like giving your 105-lb childless wife a diesel Excursion, to go to her personal trainer sessions and get her pedicures. Deep-cycle batteries are good for trolling motors or bait tanks, where you run them down during your day of fishing, then charge them back up again when you get home.
posted 04-17-2011 10:11 AM ET (US)
Batteries which are rated for high cranking current delivery from a small form size usually accomplish that by using thin plates. The design of the battery is optimized for its purpose.
Because the chemistry of a lead-acid battery is the same among all lead-acid batteries, I do not know why one would expect that a deep-cycle battery would be more tolerant of being discharged than a starting battery. The most likely difference I can infer is that in a deep-cycle battery the plates may be larger and have greater separation.
The instantaneous current available from a lead-acid battery is a function of the surface area of the plates. Having thinner plates, a starting battery can create more surface area in a particular volume of container. This also implies that the separation between plates is reduced.
It is well-known that as a battery is discharged there will be a formation of sulfate crystals on the plates. If these crystals grow large enough they could short out one plate to the adjoining plate, causing that battery cell to fail. Deep-cycle batteries may tolerate deeper discharge and the formation of sulfate crystals better than starting batteries due to the greater separation between their plates.
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