Why do batteries die?
 

I was thinking about this tonight - both the battery on my wife's Toyota and the one on my motorcycle died recently and I'm wondering what the chemistry/physics is behind this - why exactly do these things work, and why do they fail over time?

My wife's car had a "regular" car battery that you could open up a cover on the top and look inside the cells. I noticed the electrolyte (distilled water) level in one of the cells had gotten low, probably why it died. Why does this happen exactly?

My motorcycle battery was a sealed, "maintenance free" battery - why should this ever lose electrolyte? Does H2 gas produced somehow permeate through the walls of the battery over long periods of time or what?

Scientist/engineer types - edumicate away.

Checks out www.howstuffworks.com. It will tell you absolutely everything you'd ever want to know about batteries and everything else on the planet and beyond. It's one of my favorite web sites.

n'No. They die because they have no national health care plan.

Where's Michael Moore when you need him.

"maintenance free" is a bad joke in hot areas
batteries need water and "maintenance free" ones are not sealed
as a cell ages it gets higher resistance to charge current that = more heat
and more heat = lost water and lost water = dead battery

even the newer teck gel or mat type will have water lost over time
from the gel or mat by heat of charge current
the hope is it should take a bit longer

the other problem is sulfation

''16.2. Heavy Sulfation

Replace the electrolyte with DISTILLED water, let stand for one hour, apply a constant current at four amps at 13.8 VDC until there is no additional rise in specific gravity, remove the electrolyte, wash the sediment out, replace with fresh electrolyte, and recharge. If the specific gravity exceeds 1.300, then remove the old electrolyte, wash the sediment out, and start over with distilled water. You might have to increase the voltage in order to break down the hard lead sulfate crystals. If the battery gets above 110o F (43.3o C) then stop charging and allow the battery to cool down before continuing. Cycle (discharge to 50% and recharge) the battery a couple of times and test capacity. The sulfate crystals are more soluble in water than in electrolyte. As these crystals are dissolved, the sulfate is converted back into sulfuric acid and the specific gravity rises. This procedure will only work with some batteries. ''

from https://www.pacificpowerbatteries.com/aboutbatts/Car%20Battery%20FAQ/carfaq16.html