... I have had two sets of AGM's over the past 8 years, well, 1.75. I have (3) DEKA G27 batteries for my HOUSE and (1) DEKA G27 battery for my START. I did not replace the START 4 years ago, it is still going strong. I charge my batteries with the engine, I have Sea Frost Engine Drive refrigeration, which I love, as well as a Sea Frost 12V system, I run the two alternatively (usually one every other day) and the system works great. I also have a Honda 2000, I usually run this on the off day of the engine. I sort of need to run the engine for 45 minutes every other day anyhow for refrigeration, so the charging load is a good thing. And we like hot showers. If we are not moving, and that is unusual, I will run the Honda for about 2 hours every other day, then the engine for 45 minutes every other day. This is in the Bahamas. But since we do move often, the engine is on anyhow for anchoring, moving to & from, getting thru Cuts and so on, twice every day we move for 20 to 30 minutes each of those times. We rarely will motor, if at all. This year of the 3 months cruising, excluding the passages to and from the Bahamas, I can only recall two motoring days, and each of those days the sails were up and the motor was off part of the day. Anyhow, my batteries get charged often, HOWEVER, they do not get to full charge very often, and that is the key. Oftentimes when fueling or getting water at the dock, I will plug in, go have lunch, do whatever it is we need to do, and come back a few hours later fully charged. We have a TrueCharge 40 Charger.

If we had solar I think the batteries would get fully charged almost daily. That will extend the life of either choice. This Fall I am going to install a robust charging & battery system. I am likely to replace my 2000W Inverter and TrueCharge 40 with one unit, a Heart 2000W Inverter/100 Amp Charger. I think I will go with Wet Cells, either Surrette or Rolls. In our cruising lifestyle, the boat will sit for long periods of time, months, with no charge (again, if we get solar, this may not be an issue ?) so the slow, steady self-discharge of an unused wet-cell battery, due to the minute discharge currents within the battery, may be a problem. There are maintenance issues w/Wet-cells > need to equalize and check/add distilled water (which I will need to store). According to Calder, using Hydrocaps (to reduce maintenance time) with wet-cells may cause the battery to absorb more current, thereby raising temperature, until damage occurs. But if I install solar, which will keep the batteries topped off, how much maintenance will be necessary, how big a deal will it be ? I like that they can be cycled many more times than AGM or Gels, if properly cared for, which I would do. Gels won’t have fume or vapor issues, our battery area has little ventilation, and they will discharge and recharge at higher levels, so they will charge faster and voltage drop is not that much a concern than w/Wet, but how often do we put high loads on the batteries … no microwaves, limited Inverter use, etc. ? I will probably install a 400 to 500 Ah House battery bank + (independent) Starter. Maybe less if top of the line battery, which can take larger rates of discharge. For some, that may require a larger ALT > 25% of Ah + 25% to keep ALT below continuous maximum output + DC loads with engine running. Are your pulley’s correctly sized ?

I think the bottom line is if you stay on top of your batteries, love them to death, keep them fully charged, then AGM's may not be worth the extra money. However, if you think you will mistreat your batteries some, I think AGM will take the abuse and last longer, enough to justify the additional cost. Make sure your charging is properly regulated, I use a Balmar 612 and ECHOCharge Unit, and certainly install the meter of your choice, I have and like the LINK 20.

I should also add our energy consumption is on the light side, we generally average about 50Ah/day while cruising, and we don't go without much believe it or not.

Gel cells > Go with Prevailer from East Penn.

Good luck, cheers, John