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Charging Dual Batteries...

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Old 12-05-2008, 10:30 AM
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Originally Posted by Joe92GT View Post
All the battery tender does is equalize that drain, it is not a charger.
Then how is it when my tractor is dead, I hook up my motorcycles battery tender to it and come back and start it the next day?
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Old 12-05-2008, 12:50 PM
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Sure. Leave your switch in the both position and hook it up to either battery.
Yep, that will do it.
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Old 12-05-2008, 01:10 PM
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I leave the batterys hooked up all winter with the switch OFF,then in the spring if one has any crank at all I will charge it and keep it for the summer. If one is completely bone dead,out it goes and in with a new one. I have done this for years and it works will for me.Never had battery problems in the summer,Just my two cents.......
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Old 12-05-2008, 01:36 PM
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Originally Posted by ImaPoser View Post
Then how is it when my tractor is dead, I hook up my motorcycles battery tender to it and come back and start it the next day?
I scratched my head on that post too. The battery tender is all I use to charge.
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Old 12-05-2008, 02:04 PM
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I used to pull my batteries every winter and storm them inside and trickle charge them a couple of times during layup. The last 4 years I have just left them in the boat, turned the battery switch to "Off", and let them sit all winter. In the spring I put them on a 2 amp charge for 12 hours (that is as long as the timer in my storage shed allows) and they are ready to go. I got 4 seasons and 210 hours on them (Interstate Marine Cranking). Plan to replace them this spring.
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Old 12-05-2008, 07:31 PM
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Knot 4 Me,,How do you go about STORMING them inside..LOL... I'm a interstate fan also,I have sold alot of them in the last 8 or so years and I can count on 1 hand the problems i've had with'em..
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Old 12-05-2008, 08:07 PM
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Why not run your engines . If you dont relief valve spring pressure your hurting more than batteries.
I run mine at least once a week if I dont use it.I think it helps, nothing does well when sitting for a long period.
Just a different thought on total maintenance.
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Old 12-05-2008, 08:34 PM
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Wish I had a 12 month boat season, I would run my boat REAL often. Its 12 degrees here right now..... BUR....
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Old 12-05-2008, 08:34 PM
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Originally Posted by ImaPoser View Post
Then how is it when my tractor is dead, I hook up my motorcycles battery tender to it and come back and start it the next day?
A battery is made up of multiple individual cells. A battery dies and is no longer good if one of a few things happens. First, a battery if left dead will allow sulfur to build up on the plates. This sulfur blocks the flow of electrons, thus the battery can not flow current in all, or parts of each cell. The second major problem is if you overcharge a battery. Overcharging forces the gases to expand too much and be released by the battery vents. Every bit of gas that escapes drops the amp hour capacity of the battery. So, overcharging is just as bad as undercharging. Those two failures fall under improper charging, and that is 95% of the reason for early failures. The other reasons batteries fail is internal structure failure.

To keep a battery properly charged in all the cells, the voltage needs to be brought up past the float voltage to 13.6v or 14.7 (depending on battery composition) for a period of time to bring every cell in the battery to a full high charge, and prevent sulfur build up. This should happen once a month. A battery tender will not do this. With just a battery tender, the cells will become unequal, and the low ones will start to form sulfur on the walls, diminishing your battery capacity and life.

What a battery tender does to is keep the battery floated at 12.6 volts, which is what a good charger does when it doesn't need to "boost" the battery. The other thing about batteries, is that the float voltage changes with temperature. We all know that a cold battery has less power than a warm one. A good battery charger will have temperature compensation built in, so as not to over charge the battery in the summer, and under charge in the winter.

I need to test a battery tender for what is called ripple. I am not sure how much it has, but imagine its pretty rough based on what it takes to keep ripple to a minimum. Ripple is what you get when you rectify AC voltage into DC poorly. Every time the 120v crosses 0, there is a spike in the output wave form of cheap chargers. If this spike is above the float voltage of the battery then over time the battery will out gas, and loose capacity.


So to sum up:

I do recommend battery tenders over nothing at all. I have them on all my small batteries. Just be sure to get a real charger on them once a month of so.

There is a reason for buying good chargers for boats or anything with a battery, its not just a waste of money.

Last edited by Joe92GT; 12-05-2008 at 08:41 PM.
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Old 12-05-2008, 08:48 PM
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I use one tender for duel batteries and run jumper cables from one to the other
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