When talking about batteries on boats there are so many variations it is hard to get any kind of agreement on anything. Even terminology can be a bit fuzzy.

When talking about batteries, if someone says "ordinary batteries" I would take that to mean standard flooded lead acid batteries. Not AGM, not GEL, etc.

If we are talking about "ordinary" flooded lead acid batteries, they tend to come in two flavors, "starting" and "deep cycle".  The difference is real but it is still a qualitative one, and the dividing line between them is not hard and fixed except in the mind of the marketing department.

In general, starting batteries are optimized to discharge very high amperages very quickly, and for very short periods of time, and then to be recharged quickly.  The lead plates are thinner, closer together, and sometimes more porous. They are designed to discharge a minimum of their capacity before being recharged.  Because of the thinner plates, some (but not all!) tend to be more susceptible to damage from vibration and impact than deep cycle batteries.

Deep cycle batteries are designed to deliver lower power loads for longer times.  The plates are much thicker and denser, and further apart. They tolerate deeper discharges much better.  

There can also be some chemistry differences between the two, but these are the highlights.

The way MOST people use their batteries is to discharge them much deeper than 80%.  If I had to guess, I would say most people typically discharge to 60% or 70%. 50% if they work the batteries really hard. Therefore--for most--people the recommendation to use deep cycle rated batteries is a no-brainer.  Starting batteries will die in this use pattern much earlier, quickly eliminating any initial cost benefit.

But... (there is ALWAYS a "but")

If you really discharge your batteries to no lower than 80% (ever) and then quickly recharge them ALL THE WAY back to 100% then "Starting" batteries might, for you, be a cost effective approach.  Even if not "best" they will not be a disaster.  I am sure you can find people who will give you an absolutely confident answer. They probably know a lot more than I do.

Deep cycle batteries might even have a disadvantage on your boat.  Once they get to 80% state of charge, their charge acceptance rate begins to fall, and it can take a VERY long time to bring them back to full.  Topping of "starting" batteries from 80% to 100% would happen much quicker.

Most recommendations for cruising boat batteries assume a much deeper discharge than you expose your batteries to. 

And there are LOTS of other considerations and alternative, but we can ignore those for now...

Bill Kinney

SM160, Harmonie

Annapolis, MD, USA

---In amelyachtowners@..., wrote :

Hi,

Olivier told me to get ordinary lead acid batteries and don’t let them drop below 80%. With running the generator for about 1 hour each morning and then having solar panels I find that I only sometimes run the generator again in the evening.

Are deep cycle regular batteries? I did see that gell batteries are listed as deep cycle.

Best Regards

Barry and Penny

“Lady Penelope II”

Amel 54.  #17

Trogir.  Croatia