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If memory serves, I believe you need a battery in order to modulate or regulate the output of the Univolt. I also think I read somewhere that the newer converters, such as Intelipower or WFCO, do not require a battery to put out good 12 volt
That being the case, I would not invest in new capacitors. I would spend the bucks and upgrade the converter.
I pray someone else will correct me if this is in error.