Battery Selection

[MalibuC]

Time for new batteries...decision time.

Option 1: Continue with AGM

Option 2: Flooded Cell Deep Cycle

I will be going with 1 Starter and 2 House Batteries. I don't mind spending more for the AGM, however, do I need a special alternator to recharge them? If that is the case then I will go with flooded cell.

I keep reading about "gassing" and maintenance issues with the flooded cell type. In a former vessel, I used deep cycle batteries from Walmart and never had any maintenance issues, etc. These were fully discharged and recharged more than once.

What happens with AGM batteries when fully discharged?

 

[navigator97]

For a 31 Ft. boat, assuming a Diesel engine, I don't think you actually need a seprate starting battery. We have a H-33.5 with a Yanmar 2GM20F Diesel Engine and use two Group 27 Deep Cycle batteries. We alternate their use each day we are aboard. We start the engine with whichever battery we are going to use that day. No problem starting and then the engine recharges it. If a longer running time I may switch over to the other battery to top off it's charge. This has worked well for years. I have talked to a battery manufacturer and they said that starting that sized engine would be fine with a Deep Cycle Battery and no need to have a dedicated Starting Battery.

 

[Clark]

IIRC, fully discharged is down to ~50% of capacity. AGM's can handle 1-300 of those, depending on make and quality. If taken down very, very low, they can be ruined because the electrolyte cannot be replenished. I found this . .
12.75 & Above = 100% Charged
12.60 to 12.74 = 85 to 100% Charged
12.40 to 12.59 = 75 to 85% Charged
12.20 to 12.39 = 50 to 75% Charged
12.00 to 12.19 = 25 to 50% Charged
12.00 & Below = Fully Discharged
I have AGM's due to maintenance issues with their location. Given relatively easy access, I'd have gone with 2 large 6V golf cart batteries for our 280.

 

[Roger Long]

I don't think you actually need a seprate starting battery.

Roger that.

We alternate their use each day we are aboard.

Now we differ. Why would you do that? The life of your batteries is primarily determined by how deeply you discharge them. Using them together cuts the depth of discharge for any service profile in half. Starting with both batteries is easier on your starter and your engine will start quicker which is both nice and also good for the engine because turning with fuel being injected but not really running causes crud to build up in the exhaust.

Just tie them together and use them as a single battery. Less to keep track of and less chance of causing a problem by switching things around. For the price of a dinner out with another couple, you could put in a battery monitor. Once you have it, you won't believe you ever lived without it and you'll need to tie the batteries into a single bank for it to work.

 

[Benny17441]

What Roger is saying is on the money but I would go a step further and recommend you add a third battery to mantain the emergency backup afforded by a 2nd bank. If you are discharging a single bank beyond the 50% treshold you need to increase its capacity to preserve battery life.

 

[navigator97]

I get your point Roger and Benny. I will give the "Both" Batt start a try for a while this season. This hadn't occurred to me before, but it makes sense. Thanks.
Dick

 

[Maine Sail]

AGM batteries, more so than wets, like to be recharged to full very frequently or short life can result.

 

[Alan]

My mistake and disappointment....I made a quick misread of the title and thought that someone had brought up a discussion I don't think I've ever read here....Batten Selection. As with 'batteries' there are many types to choose from with various pros and cons.

 

[Dubai]

On my H326, peering down in the gap between batteries and charger I see two sets of LEDs on charger as follows :-
Battery Type
Flooded
AGM
Gel
Status
Fast Charge
Absorption
Float

The LEDs that are lit green are "Flooded" ( for battery type) and "Absorption" ( for Status). Presumably Flooded means normal lead acid type and Absorption is a normal charge.
The batteries go flat (in so far as not enough oomph to start engine) after being left fully charged within couple of weeks. Battery Isolator left in the off position and hence with no load. Batteries are obviously finished and need to be replaced.
Navigators original question about which type of battery to opt for is of interest to my own situation. Should I to try to locate AGM batteries or would Deep Cycle batteries be OK. What are the advantages of AGM Type?

Any feedback much appreciated.