On Friday, November 16, 2018 at 9:57:09 AM UTC-8, wrote:
On Friday, November 16, 2018 at 12:24:20 PM UTC-5, Dan Marotta wrote:
I'm thinking of eliminating the tail battery in my Stemme but need the
weight for proper balance.Â* I know I could replace it with pure lead,
but that's a lot of work so I've come up with a plan that would be more
satisfying and I would like comments and/or suggestions.

My thought is to discharge the battery fully.Â* It's a standard AGM that
everyone uses.Â* Then drill a couple of holes in the case and flush out
the electrolyte a couple of times with water.Â* Then fill the case up
with a highly saturated solution of NaHCO3, baking soda if I have the
formula correctly, and completely neutralize any remaining acid.Â* A
final flush with pure water, let it dry out, and finally, I could add
just about anything inert to bump the weight back up to what it was, and
plug the holes.Â* Voila!Â* A perfectly sized ballast weight.

Comments?Â* Have I missed anything?
--
Dan, 5J

Unlike a "wet cell" battery, the electrolyte in the AGM (SLA) is semi-solid (gel in mat) and flushing it out would be difficult.

Why not simply leave the battery as-is? You can disconnect it from the electrical system but there is no need to flush it. Just inspect it every few months to check whether it is cracking up or anything. And replace with another old battery after a few years. I havn't had such a battery leak yet, including some that are 20+ years old (they're not in my glider!).

One caveat: the electrolyte can freeze at low enough temperatures. To avoid that, the battery should be fully charged. Even if it's an old battery with reduced capacity you can still charge it as much as it will take. Such batteries can hold the charge for a year or more.

The electrolyte is not a gel in mat, it's just a liquid in mat and there is very little of it. If you wanted to flush it out it would be easy with plain water. You are likely confusing the common VRLA/AGM (Valve Regulated Lead Acid/Absorbent Glass Mat) battery with a "gel" battery, which almost nobody uses today. Thickening the electrolyte in an AGM battery would reduce performance.

Just leave the battery as is. There is likely no issue with freezing since there is so much air space in the mat electrolyte carriers. I've frozen multiple VRLA/AGM batteries for testing. And there is such little electrolyte in these batteries will be irrelevant for W&B issues.