I think the original question in this thread was: "Why are new
batteries no longer "maintenance free".
I agree with the other people in here that stated that supposedly
"maintenance free" car batteries still had removable caps by which they
could be maintained. I was at my local battery shop once having a
battery I had purchased from a local auto wrecker tested. I wanted to
make sure the battery was in good condition while the sales person at
the auto wrecker would still remember me if it wasn't in good shape.
Anyhow, I thought what I had was a totally maintenance free battery
because I could see no way of opening it in any way, but the guy at the
battery shop prised two plastic covers off of it that I would have sworn
were part of the battery case.
In one of the battery web sites I linked to in the thread that asked the
question "What happens when you recharge a battery" they said that as a
battery recharges and the soft sulfate coating on the lead plates
disappears, there's hydrogen atoms produced at one plate and oxygen
atoms produced at the other in a process very similar to the
electrolysis of water. That web page said that so called "maintenance
free" batteries simply had more water added when they were manufactured
to allow for the amount of water lost from the battery during it's
But, I couldn't imagine how water could be lost through the plastic
case, but I can easily imagine how hydrogen gas could be lost through
the plastic case, and if hydrogen is lost, then you lose water, even if
you have excess oxygen gas in the case.
In one of my corrosion classes years ago in mechanical engineering, we
learned about a process called "hydrogen blistering" where pipes
carrying hydrogen gas, natural gas (methane) and even just water, will
in fact form hydrogen bubbles right in the steel wall of the pipe.
These bubbles are full of hydrogen gas. In chemicals like hydrogen GAS,
or methane or even water, the molecules are breaking apart and reforming
all of the time. When those molecules come apart, sometimes hydrogen
atoms end up migrating into the steel wall of the pipe carrying those
fluids. Then, the hydrogen atoms will often find a tiny void around an
inclusion or imperfection inside the wall of the steel pipe, and those
hydrogen atoms were form hydrogen gas when they bond to another hydrogen
atom, greatly increasing the effective volume those two atoms occupy.
As the hydrogen atoms accumulate at these inclusions and form hydrogen
gas, you get bubbles of tremendous pressure that actually cause blisters
to form in the wall of the steel pipe. The only repair is to replace
the damaged pipe.
'Different Types of Corrosion: Hydrogen Blistering -Causes and
Prevention. WebCorr Corrosion Consulting Services, Corrosion Short
Courses and Corrosion Expert Witness. corrosion types, corrosion forms,
pipe corrosion, generalized corrosion, pitting co'
And, I'm thinking that if hydrogen atoms can migrate through the steel
wall of a pipe carrying hydrogen, methane or water, they'd have no
problem passing through a plastic battery case. And, of course, if you
lost too many hydrogen atoms from the battery case, that battery would
be running out of water.
Perhaps the new batteries have caps on the cells simply because they
were finding that the old "maintenance free" batteries were dying due to
lack of water simply because the hydrogen gas produced in the battery
upon recharging was being lost as a result of it seeping right through
It's only a guess, but it's my best guess.