Do Hydrocaps Really Work?

by Steve Dashew

BEOWULF has been sitting at Atlantic Yacht Basin in Norfolk, VA for the past two months. She's had her Trace inverter connected to shore power, acting as a battery charger. Before we left her we topped off the batteries.

We've been using Hydrocaps for 15 years to reduce battery water consumption and help keep the battery tops and terminals clean of acid buildup. They seem to work, but it is always nice to know for sure. So we decided to conduct a "scientific" experiment. We replaced one of the Hydrocaps with a normal cap. This morning, when I checked battery water level the 11 Hydrocaps were topped off. However, the single cell with a normal cap is showing the top of its plates--Hey, these things really do work!

On a related subject, the battery tops were spotless nine months ago. They still are. That's also a function of the battery caps, and the fact that all terminals are heavily coated in Vasoline.

This article elicited a response from one of our readers, which we've posted here:

Hi, I just finished your article on Hydrocaps and am considering buying some. However, the retailing website I found says that they should not be used when "equalizing." I'm not sure what this means or whether it takes place during typical charging, either by engine or shoreside battery charger. Any idea what they mean? Thanks, Jeff W

Hi Jeffrey: The website you found is right. When you are equalizing your batteries - which you should do periodically to keep them in good shape (more data on this in Offshore Cruising Encyclopedia) - they give off alot more gas than normal. This creates so much heat in the Hydrocaps that they will deform or melt. We ssimply remove ours for the bymonthly equalization that we do on Beowulf. Regards - Steve Dashew

(added 31 August 01)