RE: Sealed battery in pressurized compartment - a solution?

["asmyth" <asmyth@hsomail.com>]

Hi list,

I spoke to the technical folks at a couple of battery manufacturers and
thought you may find their suggestions interesting.

To recap, if your application requires more than 90 foot diving depth and
for whatever reason you can't place batteries in the hull or in a hard pod,
then you have to pressurize the battery compartment. With conventional
batteries its not a problem, but the question was how to do this without
squeezing "sealed" AGM or gel batteries.

The technical guys pointed out that if you drill a hole in one of these
batteries, oxygen in the air will react with the contents. The reaction
would not be violent (i.e., not dangerous) yet would probably produce enough
heat you could feel it. Over a period of "days, not minutes", the reaction
would oxidize the plates and ruin the battery's performance. For this
reason, a hole and pressurizing with air is out.

However, one manufacturer suggested drilling the hole and pressurizing with
Argon. I got a second opinion from another manufacturer, who couldn't think
of any reason it would not work, although he cautioned neither did he know
of it ever being tested. He recommended pressurizing a battery with Argon,
and then measuring its performance over a period of several weeks to ensure
it does not degrade. One negative possibility is that the battery could
gradually dry out. But at least now I've got something to test.

-Alec

> -----Original Message-----
> From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org]On Behalf Of asmyth
> Sent: Saturday, June 26, 1999 3:47 PM
> To: PSUBS
> Subject: Sealed battery in pressurized compartment
>
>
> Hi guys,
>
> I am thinking of putting sealed AGM batteries in a pressure-compensated
> compartment. I believe the batteries have some kind of gas vents, but I
> imagine they are designed to vent only outwards. As the
> compertment pressure
> increases, this will put a squeeze on the battery cases.
>
> Is this as simply as drilling a very small hole in the top of the
> batteries?
>
> -Alec Smyth
> PS: dive depth is unknown as yet, but presumably quite deep (its not a wet
> design)
>