Micro Brix wrote:
> Why not just use a relay to connect the batteries whenever the voltage is
>> over  some preset voltage? I've seen this method used quite successfully
>> in commercial products.
> 
> How do you disconnect then?  If both batteries are connected, then the
> voltage stays up till both are somewhat discharged.
> I was also looking for it to perform regulation, so that my gel cell
> wouldn't necessarily be charged by the comparatively rude and crude vehicle
> charge system.

After the car shuts off, it won't stay at 14-ish volts for very long, at 
most a few seconds, and that won't hurt anything.

Agreed about the less-than-perfect charge algorithm of the car, but if 
you only need 3 years service life on the gel cell, it's good enough.

I had a UPS made by Best Power, and the battery lasted 8 years. I tested 
it every year, and was amazed to see it still could keep the test load 
up for a decent amount of time. Especially when my Tripp-Lite UPS 
regularly split its batteries open every two years.

Cheerful regards,

Bob
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