Re: (ET) Update my my old "cooked" Trojan batteries

["David Roden" <etpost drmm net>]

On 28 Aug 2009 at 7:36, David Barden wrote:

> and what's the best indicator of a battery's state of charge  specific
> gravity or at rest voltage?

SG.  Voltage is better than nothing, and we have to use it with valve
regulate batteries since we can't get to the electrolyte -- but it's a
relatively unreliable and inaccurate SOC measurement.

>
> my 2 yr old interstate pack have never registered an sg of greater that
> 1.265 no matter how hard I charge them(lately that's 2.45v per cell). 
> Is this natural? 

That's normal for a deep cycle battery.

> I've other packs that when fully charge are at 1.300.  will different
> brands of batteries use different acid concentrations?

Yes.

>
> I guess the good side of that low sg is they won't die of grid
> corrosion!  ;^)

Exactly!  A battery designed to have a relatively low full SG is called a
"starved electrolyte" or "acid starved" battery.  That strategy also helps
prevent over-discharging the electrodes.  It's the secret for East Penn gel
batteries' long life even in EV use.  For those batteries, a 100% discharge
is really only about an 80% discharge for the electrodes.

The downside of a starved-electrolyte battery is that its published 
capacity
 (and to some extent its usable capacity) is lower.


David Roden - Akron, Ohio, USA

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