Backyard Aquaponics
A place to discuss aquaponics

BW that is a charge pump power supply, but doesn't boost the voltage. Have you heard of Rube Goldberg ?

I love everything Rube Goldberg

Who doesn't ?

Beware "sticking a resistor across the battery". An AGM battery commonly has very low internal impedance, some of the Century Yuasa ones that I used to use for remote high-power communications sites had an internal impedance of 7 miliohms.. (7x10^-3 ohms). So to calculate fault current, you do I = V/R and get 13.8 / .007 = 1.97x10^3 Amps. Yes, nearly two thousand amps! If you drop a wrench across the battery, it will weld itself there.. wire will vaporize. Fault current can be dangerous, so please don't entertain your friends idea.. also it's VERY inefficient.. you'll be throwing power away for nothing. Please consider the other option, adjusting your UPS voltage sensing to match where you want the battery to sit. But more realistically I would say that unless you have very strict instructions from your battery manufacturer not to float the battery below 2.35V/Cell you'll be fine. Don't drag the battery voltage below about 11.1VDC and don't exceed 14.5VDC or you'll cook it. Past that I personally wouldn't worry that much. Except about fault current. You're going to want to put fuses on both terminals of that thing and keep the posts covered.

Cheers!
KS