More about Glider Batteries:

My club's gliders use Gel batteries, probably because they fit the
mounts so well, but mostly the private gliders use a battery type with
many names, I guess it's an SLA (Sealed Lead Acid) except it's not
really sealed. I started to call it an AGM (Acid Glass Matt) which it
has, but suddenly it started to be called a VRLA (Valve Regulated Lead
Acid). Anyway they are very interestingly made. Although they look
sealed many of these have a separate and tightly fitting top which is
glued on only at the short sides, (the Valve Regulated gas being
allowed to escape through the unglued long sides) and this cap can be
pulled off pretty easily exposing the sub-assembly consisting of small
recessed nipples rising from the center of little 'moats' that have a
fabric packing in them, I guess to absorb any acid that gets out of
the valve. Each of these little nipples has a rubber cap which forms a
one way valve. Pictures of this can be found he

http://picasaweb.google.com/BrianDG3...laneBatteries#

As far as I can tell the battery exhausts gas (and/or liquid) whenever
the internal pressure rises very much beyond the ambient, but seals
tightly when the internal pressure is lower than ambient. When the top
is removed the caps are dished down into the nipple from negative
pressure and when you pull the cap off there is a considerable hiss of
air flow into the battery. So, although they are valve regulated I
don't think they 'breathe' much, at least not in.

Also in that group of photos is a housing I've made, different from
but based on an example I saw Darryl Ramm make, that forms a handle,
protects the battery terminals, holds a Klixon aircraft rated circuit
breaker and two Anderson Powerpole connector sets. Using clear Lexan
for the top is a trick from hospitals, they will sometimes make
electrical devices out of clear polycarbonate- you can inspect the
terminals that way and see a failure developing. Also makes it easier
to work on. Having two outputs is very useful as well.

Brian