Battery charging

[Abbeysdad]

My new, used boat had a lame starting battery hooked to the trolling motor (I think a junk battery went in where a better one used to live and when the previous owner traded up, he swapped in an old battery).
So I replaced it with a big yellow max deep cell EverStart. The trolling motor battery is not connected in any way to the main battery.
I have been pulling and charging the TM battery after every time out, but haven't been charging my main battery (allowing to be maintained by the motor alternator/charging system) which (knock on wood) seems to be working okay....but just wondering...should I be routinely charging the main battery? Or maybe a better question is what do you do?

[nofearengineer]

Originally Posted by Abbeysdad

My new, used boat had a lame starting battery hooked to the trolling motor (I think a junk battery went in where a better one used to live and when the previous owner traded up, he swapped in an old battery).
So I replaced it with a big yellow max deep cell EverStart. The trolling motor battery is not connected in any way to the main battery.
I have been pulling and charging the TM battery after every time out, but haven't been charging my main battery (allowing to be maintained by the motor alternator/charging system) which (knock on wood) seems to be working okay....but just wondering...should I be routinely charging the main battery? Or maybe a better question is what do you do?

If your engine's alternator is atrong enough, you should have no need to charge your cranking battery, as long as it doesn't sit for a while. I always check the voltage on mine before I leave for the lake. As long as it is over 13 volts, I know I'm in good shape.

[Bassmagician]

I have owned a boat of some kind for 25 or so years. I recently purchased a battery charger that you can hook up to the battery and it will show you the percentage of life you have left and also the voltage on a digital read out. I give the main battery a check to make sure the motor has left it at 100% at the end of a day of fishing. You may allready know this but I never charge my trolling motor batteries above a 2 amp. (trickle) charge unless I plan on using them the next day. It seems the slower you charge a battery the longer it will hold a charge. Also makes them last a lot longer.

[Abbeysdad]

I have a similar new charger (Shumacher Ship 'n Shore) but I don't think the percentage left in the starting battery after a trip out is 100%, more like 75%. although the voltage is 12+ and it's always (again knock wood) had plenty of cranking amps, even with some hard starting (like when super newbie wasn't using the choke properly when cold or the time recently I forget and didn't prime the fuel bulb!).

Also a 2 amp charge is for lawn mower type batteries and not recommended for large deep cell batteries - they recommend the 10 or 15amp charge. Although I have also read that charging at lower amperage extends battery life which would suggest a 10amp charge for a larger deep cell marine battery.

footnote: I actually had some dialog with Shumacher tech folks. I saw that my charger stepped up to 100 percent and kept on charging - I was afraid it was overcharging but they assured me that this was normal and I should let it keep running. I found that it may continue charging two hours+ after it reaches 100%.
(The calculation for percentage should be taken with a grain of salt because of how it's done)

[Bassmagician]

I have peformed several test with the carger. I used my Fluke 87 multimeter to check the batteries and didn't depend on the charger as much. You should have 13 to 13.5 volts on a fully charged battery. After a hard day of fishing in very swift current the trolling motor on high most of the day, the trolling motor was strong enough to pull the current 10 hrs., when I used a trickle charge. Then I charged the batteries on the faster 10 amp. charge and fished in the same location and I only had about 6 hrs. that the trolling motor would pull the current. I have performed the same test with the 15 Amp. & my onboard charger, with close to the same results. I have stopped using my onboard charger (unless I have to) just for this reason. Nevermind the recommendation on using the 2 Amp only on a lawn mower battery, that just a recomendation by the manufacturer of the charger. Now on the other hand if you use the higher amp charges on a small lawn mower battery, it will ruin it. NOT GOOD. It will not harm your deep cycle batteries to charge them with a trickle charger, only help them.

[Abbeysdad]

I'm thinking that companies in the business of making battery chargers have done far more DOE's and product testing than any of us ever would or possibly could.

I'm also thinking that a fully charged battery should deliver pretty much the same rated amp/hours, regardless of how it became fully charged. I've never seen any claims like those you observed relative to charge rates. I'm wondering if in the 6hr10amp charge example whether the battery was fully charged.

I have read that batteries should be slow charged to promote longevity, however I have also read that this means the battery should be charged at a rate that is less than 20% of it's rated amp/hours capacity AND that the charger used should be able to fully charge the battery in a 10-12 hour period.
So for my big yellow max (125 amp/hours) I should charge at less than 25amps. When it was at 70%, it took about 10 hours using a 15amp charge. I'd expect a 10amp charge would take several hours more (16~hrs) and a 2amp trickle charge would be perhaps (60hrs~) days. (But these are just relational equations) - I'm not sure a battery of this size can even be effectively charged at 2amps.

So technically, applying the 20% rule, I should be able to charge my 125 amp/hr deep cycle at either 10amps or 15amps with no ill effects.

[Bassmagician]

I don't go by numbers on a piece of paper or a web site. I just have to see things for myself. You know trial & error. I have made a few goofs in my life but I have also picked up realy good knowlege by doing so. Just a sugestion.

[nofearengineer]

Bassmagician, I think your ideas are good, but your methodology might be faulty. Clearly, the battery is being charged better with a trickle method. However, it may be simply because that particular charger works better in trickle mode, and not due to the nature of lead acid batteries in general. Or maybe without realizing it, you used the battery a little harder the one day. Battery capacity is not a straightforward, linear process. A battery used twice as hard does not last half as long. Sometimes using a battery only 10-20% harder will decrease the capacity by 50% or more. It all depends on the particular battery and the application.

All that being said, I would agree with you about only charging a battery as fast as you need it again, within reason.

[Bassmagician]

I am no engineer, nor will I ever be. But the first year I had my current boat I charged my batteries with the 10 amp. onboard charger and used a 12 amp charger that I used on my previous boat. The batteries lasted a little over a year.
The next set, maybe a few months longer. I purchased a charger that had a 2 or 10 amp. switch by the sugestion of a friend and started using the 2 amp setting only. The third set that I purchased lasted 2 years.
I fish eleven months of the year, almost every weekend and never let my batteries stand uncharged. I have gone through a couple of chargers and only three sets of batteries in the past 6 years. It stands to reason ( in my mind ) that the trickle charge has helped the battery life in my case. :-)

[Abbeysdad]

Setting aside for a second this new claim of longevity, quite unlike the first, I think the success of a 2 amp [trickle] charge may depend on the battery and the charger. My Shumacher Ship 'n Shore 2/10/15amp charger specifically recommends against using the 2amp charge as a "trickle charger" for larger batteries. I believe is has to do with programmatic way in which it charges. I also wonder about the effectiveness of a very low charge. My new big yellow Maxx Everstart is an 875CA/125Amp/Hr Deep Cycle - I have tried to charge at 10amps, only to bump it up to 15 after a couple of hours where the percentage had not increased at all. I will leave it at 10amp next time and see what happens, but based on the mfg. caution against the 2amp charge, just can't go there-
As far as battery longevity, I've read several recommendations (some may apply more for deep cycle marine batteries):
1) lower amp charge is better (not to exceed 20% of the batteries rated amp/hr.)
2) Discharge no more than 80% with no more than 50% discharge considered a best practice.
3) Recharge soon after discharge as even a 24hr wait can reduce longevity.
4) New batteries should be charged right away and babied through the first several charge cycles with only slight discharges.
5) Batteries should be charged before storage and routinely recharged during storage.

Btw BM, I'm jealous that you can fish as much as you do!

[Abbeysdad]

getting back to the original question, I guess I won't worry so much about charging the starting battery, unless I discover a problem/need to.

[Bassmagician]

Nice rig by the way, I hope you have a lot of fun & safe days on the water with her.
A good friend told me once just before I purchased my fist boat "A boat is a hole in the water to throw money into". I have found this to be a true statement. Good Bassin'.

[Abbeysdad]

Originally Posted by Bassmagician

Nice rig by the way, I hope you have a lot of fun & safe days on the water with her.
A good friend told me once just before I purchased my fist boat "A boat is a hole in the water to throw money into". I have found this to be a true statement. Good Bassin'.

Thanks BM - She's a fantastic first boat for both fishing and touring. Imagine my surprise to find her in my garage the day before my 55th birthday!
And the statement seems very true, ESPECIALLY at first with all the stuff needed to make her safe 'n legal on the water!

[Bassmagician]

Everyone should have a pastime like hunting & fishing. It is relaxing & allows you to clear your mind of the crazy world that we live in. Money is just an object that comes and goes, but every trip in the outdoors leaves you with memories that last a lifetime.