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Old 06-07-2015, 02:16   #16
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Re: Gel batteries, signs of imminent death?

Originally Posted by mitiempo View Post
As far as I know it is not resistance that is needed, but voltage. If the charger sees zero voltage it remains inactive. By paralleling another battery you are providing that needed voltage.

I fail to see why an Optima or any other lead acid battery would be different as far as charging one with zero voltage is concerned - regardless of which form the acid is in.
According to Optima; their AGM (Absorbed Glass Mat) batteries have a very low internal resistance which partly accounts for their good performance. So when they are "flat" there is an open circuit. I.E. no current can flow through the battery. A flooded cell battery has a higher internal resistance so even if it's "flat" current can still flow. The battery that was completely discharged in my car is actually an Exide AGM. With the Exide I still needed to use another battery in parallel to start the charge process. If you do a google search you will find out more.
I have been very pleased with my 3 Optima AGM batteries in my boat and Exide AGM in my car. I also have another smaller Chinese AGM on a separate circuit with solar only charge for my boat instruments. This is to avoid voltage spike damage from the inverter, water pump, Autohelm, electric fridge, and alternator in the house battery circuit. I previously had trouble but that's too long a story.

Getting back to the original question about gel batteries. I previously had expensive German gel batteries in my boat (can't remember their make at the moment). They only lasted 2 or 3 years. Since then I discovered that gel don't like being overcharged. I did not have a separate regulator then, just the standard regulated Hitachi alternator output. I now suspect that the alternator voltage regulator needed a lower setting then for my gel batteries. Maybe 13 / 13.5 v instead of 13.8 / 14 v??

I now have a Next Step, (made in Seattle) smart regulator for my boat AGMs which as I earlier mentioned are 12 plus years still going strong except the start battery that I have just replaced after about 11 years. That's my experience anyway. I'm not suggesting one type of battery is better than another, just that each needs correct charging.

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