Don,
The ‘Starting’ batteries referred to in the looper forum are required for some diesel and large (45ft) gassers. You’ll find a ‘Dual Purpose’ battery that can provide the specs required by your outboard engine maker. Then, that same battery can help power all your overnight needs while anchored out or combined with a House battery. A Starting battery can put out a huge slug of current for a short time, but will be damaged by lower demands overnight, so there is no advantage, but significant disadvantage, in using one on an outboard trailer boat.
After meeting the outboard starting specs, the next question is how much will you anchor out, what power draws will you have all night, and how will you recharge the drained batteries?
A battery monitor or ‘coulomb counter’ is almost mandatory to figure that out and gives Ah in and out, watts, an accurate State of Charge %, etc. I installed this one; fancier versions even have Bluetooth. This is a DIY install for most folks with basic 12v skills. In general, you don’t want to drain your lead acid batteries more than 50% (roughly 12.2V but the meter is more accurate).
https://www.victronenergy.com/battery-monitors/bmv-702
For long distance cruising, I’d avoid a boat that doesn’t have a 110v shore power panel with a battery charger and a couple of 110v outlets including one for a 12/110v fridge at a minimum. For the most basic 12v systems, the typical fridge with Danfoss compressor will be the biggest energy hog. After the last opening before bedtime, we turn the thermostat warmer…it won’t need to run as much but still keeps the ice cube trays hard frozen if the door stays closed. Our other loads are a couple of LED reading lamps, a small Pure Sine Wave inverter to power the laptop, the LED anchor light, and sometimes a 12v fan or two. On our Tenn Tom adventure, the SOC was 100% on all three Group 31 FLA batteries at sunset. At sunrise the Combined S Eng + House SOC was 86% each day with the P Eng isolated. A simple rooftop Renogy 100w solar panel charged them back up to 100% before 3PM. That’s an easy DIY install under $250 with the circuit breaker and Victron MPPT controller, assuming you don’t end up putting a bunch of other stuff up there that shades it.
Other common CD recharging options include running the outboard at fast neutral, or carrying a Honda generator.
I deeply respect Bob’s lithium systems knowledge and expertise. We hope to run Cat O’ Mine competently on the road and in the water until age 80, which is only 10 years away. Until then, our strategy is to buy FLA-31 batteries ($112 each on sale) and replace them every 36-48 months from mfg date, regardless of how well they pass a load test, if we will be cruising in remote areas like Georgian Bay.
Lithium is the future, but the future is not yet here. Even the standards are evolving or not even set yet.
In our experience with 13 trailer boats over 40 years, a typical AGM will last 6 to at most 10 years, a typical FLA last 3-5 years and no experience with Lithium batteries.
Good luck and tap the Brat experts in your journey to find a CD right for you and your crew!
John