The general rule of thumb for flooded lead acid batteries is to not take below 50% state of charge.
Group 24 starter battery
- Thread starter skunther
- Start date
Starter batteries can’t be as deeply discharged as deep cycle without doing permanent damage. But I think it’s unlikely the windlass is doing serious harm. The load is large but very short term. Even if it’s 120 amps for 2 minutes that’s only 4 amp hours - hardly a deep discharge. On top of that the alternator is generally running when the windlass is being used, offsetting at least some of the load.
The standard rule of thumb I was always taught for a flooded lead acid battery was you could draw it down to 75% state of charge. In the marine world they talk about 50% state of charge.
The actual answer is complex. "Before doing damage" depends upon amount of discharge, temperature, and length of time at the stated discharge level.
Discharging below 50% would certainly not be recommended.
dj
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,832
No.
Basic anchoring skills have you running the engine (coincidentally charging the battery) while you are setting or retrieving the anchor.
Not knowing how your battery banks/charging/switching situation is set up, I don't know why it doesn't make sense to simply put in a starting battery for starting and rely on deep cycle batteries for house loads. Deep cycle batteries normally are perfectly fine for starting our small diesel engines but you have other concerns about starting. That said, I see no reason for a "dual purpose" battery. They are a poor man's compromise .... not good for starting, not good for deep cycling, either. If you have a reliable deep cycle bank for house loads, then why would you be thinking about your starting battery as an auxiliary for house loads? If you don't have a reliable house bank, then solve that problem independently.
In your situation, you are asking about the best battery for starting, even if it is a temporary concern until you resolve your hard-starting issue in the off-season. Then don't get distracted by peripheral concerns. Just get the best battery you can for starting. It's going to serve you the best way in the long run anyway.
Some folks say "don't use the start battery for the windlass". I say it may depend on normal circumstances. I use my start battery to power the windlass and see no reason why not. With my set-up, I use the start battery exclusively for starting and the windlass and my deep cycle bank is used exclusively for house loads. There is no reason in my mind to mix this up in any way.
In your situation, you are asking about the best battery for starting, even if it is a temporary concern until you resolve your hard-starting issue in the off-season. Then don't get distracted by peripheral concerns. Just get the best battery you can for starting. It's going to serve you the best way in the long run anyway.
Some folks say "don't use the start battery for the windlass". I say it may depend on normal circumstances. I use my start battery to power the windlass and see no reason why not. With my set-up, I use the start battery exclusively for starting and the windlass and my deep cycle bank is used exclusively for house loads. There is no reason in my mind to mix this up in any way.
One of the reasons not to use your start battery for the windlass is because the start battery must serve both starter and windlass - those locations are typically far apart on the boat. Both the starter and the windlass are high current engines. It's usually hard to find a spot for the start battery to supply both as needed for those engines without expensive large cabling.
dj
Not True for Hunter sailboats.
Start Battery is for many high Amp needs.
Mine does Electric Winch, Genset starts, Bilge Pump, Windlass and on Bigger Hunter's a Bow thruster.
Check here for Expert Advice...
Marine How To - DIY for Boaters - Marine How To
Jim...
PS: Mine from Walmart = $90 starts 50 HP ENGINE
Sure, if your boat is designed to place your start battery in a location that works for all the above.
Actually, your point is one of the reasons I like many Hunter sailboats - among other reasons.... (Still can't understand the Hunter "bashers")
But a lot of boats are not designed to have the start battery placed in such a strategic location.
dj
That's a fair point ... but my start battery is also located forward closer to the windlass than the engine, where Catalina placed it. I'm generally saying that it does depend on the individual circumstance. I know others who will contend that you wouldn't want the windlass to deplete the start battery, but there are counter-arguments at play there, too. Many larger boats will have 3 or more battery banks to adapt to these issues.
We are in complete agreement.
My boat is one where I do have three battery banks; house bank, start battery, bow thruster/windlass bank.
dj
I probably don’t need to point this out, but I will anyway…
50% does not mean 6 volts!
here is an AGM battery SOC chart from MaineSails website…
If you arr seeing anything u dear 12 volts, you are below 50% SOC
I believe this is resting voltage, so you would have to let the battery sit a while with no load to get an accurate reading.
Greg
When using voltage to estimate SOC, remember it is estimating the SOC of the current capacity, not the capacity of the battery when new. All batteries lose capacity over time and cycles. In terms of a starting battery, the lower the capacity the less it can deliver when cranking an engine.