help me pick out the right type of diode

I cannot imagine any diode circuit that would prevent a bank of paralleled SLA batteries from discharging into one with lower than the average terminal voltages of the remaining batteries. Show us a schematic of what you have in mind before going off on a quest to find "the right diode (type and size) for the job."

 

Hop,

I know he did not say this, but I think he is talking about a diode between the + terminal and the bus bar, so the batteries are paralleled only through the diode, which is a common enough circuit.

The diode needs to handle the full current you expect on the load, and, depending on how high that is, might need to be heatsinked. Schottky diodes are a little better for this since they have a lower voltage drop and therefore dissipate less heat at the same power.

Bob

 

Thanks, Bob. For some reason (senility?) I didn't even think about using isolation diodes in series with each battery. That's a pretty good solution if you don't mind the power waste under load. As you said, the OP needs to know the full load current, and should probably use a Schottky power diode to minimize forward conduction power losses under load. And of course the reverse voltage specification of the diode should exceed the battery terminal voltage. The OP needs to provide more information about battery voltage and maximum load current. Cree makes some high power silicon carbide Schottky diodes, so I would look there first.