NoPistons -Mazda Rx7 & Rx8 Rotary Forum

Quote:

Originally Posted by 89 Rag' post='568693' date='Jan 1 2005, 02:54 PM

The ones that stay charged are fine, but the battery I had in my 7 and the one's in my father's toys only seemed to last till the sixth recharge, after that they would never hold a charge, not even enough juice to make the under hood light come on. I can't say it's a fact of all Optima batteries, only my experince from the 20 or so I have played with in the last 5 years.

All standard automotive batteries are like that. Everytime you drain them, they lose capacity.

Automotive batteries are a lead-electrolyte solution... sulphuric acid with some lead plates tossed in. The lead plates in car batteries are spongy, and very porous. This helps to increase surface area for the acid to react with. Well... when you fully discharge these things, a bunch of the lead crumbles and fells to the bottom of the battery. You lose a big chunk of your reacting surface. Do this five times and you might as well throw out your battery.

Deep cycle batteries work the same way: lead and aicd, except that the plates are solid lead. They are generally a little less powerful for equal weights, but they can be discharged MANY times... hence their use in marine starting applications. When you drain a deep cycle battery completely, the outter layer of lead on each plate crumbles and falls off, but the total surface area of reactable surface reamins relatively unchanged. Discharge a deep cycle battery enough, and eventually, you'll run out of plate, just like a standard battery.

SO...... what does this all mean? If you think you'll be draining your battery, get a yellow top (deep cycle). If you have a good alt and don't leave your accessoriies on, get a redtop. And if you're storing any battery... buy a self-monitoring trickle charger.