Very true. Care begins on the water. By using 4 batteries, you are spreading the wear & tear that would otherwise kill a single battery (12v TM) or pair of batteries (24v.) The backup batteries allow you to switch before discharging the first battery (or pair) too deeply. Deep discharge reduces a battery's life expectancy--measured in charge/discharge cycles, not years. Calendar years may be important from the budget perspective, but number of cycles (fishing trips) is a better way to judge the true value of a battery.
When I ran a 12v TM, I got about 100 trips out of a WalMart deep cycle marine battery that cost less than $90. Convenience, warranty, and a cost-per-trip of $0.90 seal the deal for me!