J.M.,
We have three group 31 AGM (upgraded from 27) under the transom seat. I can’t imagine group 24’s on a TC255 with a fridge. AGM’S have to be ‘secured’ but not totally encased like wet cells. Some boats used for charter diving or heavy fishing have converted that space for compressors or live wells. PS my original fridge died early due to no ventilation in the Nav seat cabinet.
We have one House battery (which gets a workout every night at anchor on every cruise) and a separate Engine Start battery for each engine. Those two slackers each work for about two seconds each moving day. Seems odd, but each boat is often wired differently. Our windlass runs off the House battery, which gets no charging when underway unless I manually Combine it with an engine battery. (I don’t have an ACR due to a unique feature of the Blue Seas PS12 40-amp charger I like).
On average for us, two nights at anchor will consume the 55 amps max one should extract from a 105 amp group 31 battery. It helps to turn the fridge thermostat warmer at night when you’ve shut the door for the last time. The Victron 702 is invaluable as a coulomb in and out counter and worth the extra cost over the 701.
A high quality battery charger is needed to top off what the engines don’t (the last 20%). The standard Guest 5/5/10 amp is (ahem) not in that group. Even the highest quality batteries can not meet expectations with a sub par charger when on shore power.
Over the past 40 years on trailer boats, I was disappointed with the performance of flooded cells as well as AGMs from Optima, Odyssey and others averaging 36-48 months before failing a load test (at which time you should replace all three, or the weakest will bring down the strongest). They all made it hard to get warranty replacement ie ‘ship it to us so our engineers can examine it etc’ and in the interim you have nil. Also, no one will replace the other two good batteries under warranty.
In 2017 I installed three Northstar AGM 31 which are still testing strong at a record five years (rated for 800 discharges to 80% with a three year replacement warranty). However, they’re now $500 each. Lifeline is even more, but they have an excellent reputation in military and aviation use (if it’s good enough for an F-16).... That still won’t get you enough amps for another night at anchor. Rolls/Surrette 6V golf cart batteries might last even longer.
You could run the engines for a while for some bulk absorb charging if you don’t want to deal with a Honda generator on board (we don’t).
I concur with Jim Healy that soon a lithium drop-in replacement for boat batteries will be routine, but we are not quite exactly there yet. As always, there are some exceptionally knowledgeable experts (like Thataway) who make it work just fine.
I have come to believe that the most common reason for premature battery failure is what I call “Switchcraft errors” or operator error. Especially in my case.
Mike Rizzo (knotflying) on a Ranger 27 has an interesting theory. He replaces his three cheap WalMart flooded Group 31’s ($90 each) every 36 months regardless of how they test. He presents a convincing argument that this is the best return on investment for most cruisers. And if you need to replace a battery in Montebello, Quebec on a Sunday, there’s a WalMart there and you don’t have to speak French.
I’m undecided about what to do when I finally kill off the Northstars. I don’t want flooded batteries on the boat, so maybe cheap Duracell 31 AGM’s at $220 each and replace every 48 months regardless.
I’m sure the hive will have great observations and that you need better batteries for cruising on that great boat. Which charger do you have? Also concur that the Smartplug is a good investment. Cynics will say, “Hey, all you did was move the highest risk connection from your boat to the marina power pedestal!”
Exactly.
If Santa brings you three Group 31 Lifelines, you must have been very, very good this year.
Cheers!
John
