1980-81 Mercury 115 Tower i-6 convert stock rectifier to regulated CDI?

[Old Vintage Merc]

I ran the diagnostic ladder test on my '80-81 Mercury 115 Tower of Power and the rectifier failed the test. I understand the stock rectifier has no capacity to regulate the voltage and leads to shortened battery life due to frequent overcharging. The standard rectifier is the 3 post with 4 wires, the voltage regulated CDI unit has 3 wires and the ground. Has anyone upgraded their rectifier to the improved CDI unit?
The standard Sierra replacement rectifier can be had for about $15 and the CDI one is $65, so that is a consideration too.
Thank you.

 

[johnnygjr]

If you opt for the cheaper one, you can add an accessory,Radio,GPS to use excessive voltage

 

[Old Vintage Merc]

I double checked with my reading glasses this time and I didn't have the diagram oriented correctly. The rectifier passed the ladder test. I think I'll use fish finder with speed and depth, it'll use a good amount of wattage. Would a simple amp meter suffice to keep an eye on the battery or is there a better alternative? Would two batteries in parallel help distribute the over charging?