It has been stated here several times by respected posters that recharging a deep cycle battery when it is only 70% discharged will shorten battery life.

It has also been stated by same respected persons that not recharging a battery shortly after use will shorten the battery life.

My problem is that often I go out on the lake for a few hours.  When I return the battery is at 70-80%.

do I recharge it, or leave it at that level till the next time I go out (could be a week, ususally less) to run it down to 50%?

It is a Trojan grp 27 AGM deep cycle black case TM battery.

Thank you for your advice.

avid

I once had a A/C Delco Voyager deep cycle battery (27 class) that I used on my small 2-man boat for short trips and/or small lakes.  My motor was a 12v 30-35 lbs. thrust transom-mount TM.  I was told to always recharge regardless of how much I used it, so I always did.  I did also charge on a low amp setting mostly.  That battery lasted 6 years before I ever noticed a drop in capacity or shotened running time.  So, I always recharge.  Hope that helps, avid.

dink

Unless I'm fishing back to back days, I always recharge after a day on the water.  Never had any trouble.

Avid, I found this online.  I included the link.

http://www.uuhome.de/william.darden/carfaq11.htm

If possible in a well ventilated area and at room temperature, recharge a deep cycle battery each day it is used and as soon as possible after each use. The best way to prevent permanent lead sulfation when a starting or deep cycle battery (or battery bank) is not in use, is to maintain it's State-of-Charge at 100% by continuous float charging. If continuous float charging is not possible, recharge before the State-of-Charge drops below 80%. Permanent sulfation kills approximately 85% of all deep cycle and starting lead-acid batteries not in weekly service. During hot weather, try and drive your vehicle at least once per week and in cold weather, once every two weeks. This is because batteries are perishable and the vehicle's parasitic (ignition key off) load and the natural self-discharge drain the battery. When the battery is not fully charged, sulfation occurs and the lead sulfate crystals will accumulate, harden and reduce the capacity of the battery. The same phenomenon occurs when a battery is undercharged or when electrolyte stratification occurs in larger wet lead-acid batteries. Please see Section 16. for more information on sulfation.

Avid, couple of things to make life simple, if your going to use it the next day, don't charge it, if you're not then charge it.   Normally it's best not to recharge a battery that still has 80% or more charge left on it.  Sulphation generally starts when it gets' any lower.

Now the flip side of this, even if you don't charge it for several days after using it, if you keep it stored on your charger with it in the float mode, it will eliminate any sulphates that happen to start.  That's the beauty of the High Frequency Chargers.  I've never messed with the one you have so I would check the float voltage and make sure it's 13.2 volts and check it a day or two after you connect it so it's had time to settle into the full float mode.   Just don't make a habit of not charging if it's going to get stored.   The sulphates can build up much faster than the charger can get rid of them.  It can takes two to three months for a good HF charger to bring a heavily sulphated battery back from the dead.

Thanks,

I recharge immedieatley after returning home.  Sounds like that's the best way to go.

Avid, couple of things to make life simple, if your going to use it the next day, don't charge it, if you're not then charge it.   Normally it's best not to recharge a battery that still has 80% or more charge left on it.  Sulphation generally starts when it gets' any lower.

This is totally wrong.  Always charge the batteries ASAP.  

Oh, Well, I guess I need to tell the head engineer at US Battery company, he doesn't know what he's talking about either. However, personnaly, I will still take his word

Ya'll preach so much about how great the Dual Pro and a lot of these other battery chargers are that don't have a float mode, they drop the voltage lower than that before they turn back on.  Guess they don't know what they are doing either.