Date:         Thu, 22 Feb 2007 14:32:14 +0000
Reply-To:     dhaynes@OPTONLINE.NET
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject:      Battery Myths-including deep cycles
Comments: To: syncro@yahoogroupsw.com
Content-Type: text/plain; charset=us-ascii

Interstate Batteries-Interstate does not build there own batteries. they are a marketing and distribution company. Their batteries are actually made by Johnson Controls. Yes, the same people that make the Wal-Mart Ever Start. I got this first hand from the folks at the Interstate Hospitality tent at the Daytona 500 where both Interstate and Johnson Controls reps were present. I was there as a guest of Hawker Batteries.

Connecting an Auxiliary battery to the main battery for charging-If the house battery is discharged, current will not suddenly rush from the main to the discharged house battery. The main reason a battery loses the ability to deliver current as it discharges is because the resistance of the battery increases. Not only can't it deliver current, but it will resist accepting current also. Yes, some current will transfer but it does not happen like water flowing between two pools. As the alternator is a voltage regulated device, as long as the voltage is above the level of both batteries, both will get charged to their own needs.

As for charging, any battery used for deep cycling will require additional maintenance as compared to a starting battery which will typically have ~3% of its capacity used. Under charging will cause sulfation. Over charging will cause oxidation. The ideal voltage is a compromise as these effects overlap. Deep cycle batteries will need to be off gassed to stir the electrolyte so the acid does not stratify at the bottom. Stratification causes high voltage readings but limited current availability and plate damage. In addition, over time, equalization is needed to get all the cells at the same charge level. All deep cycle applications need a smart charger there at some point. Even used periodically, this is needed. Ideally, you want to operate the battery from 50-80% state of charge with the periodic full and maintenance cycles.

Battery combiners offer the advantage that a single charger can maintain both the house and main battery with limited additional controls. Relay devices work just fine. A large 150 amp relay costs about $20. Sure power isolators and other fancy devices offer limited benefits.

I can add a bunch more but I gotta go for now.

Dennis