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Battery Tenders

M35A2-AZ

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I have read some threads about using a Battery Tender on the batteries, but would it be better two use two 12v tenders or one 24v tender?
Thanks!
 

doghead

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On a M35a2(2 batteries in series with one alt), I think 2-12 volt chargers is best.
 

emr

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A big yes, But...a 24 volt works well and is just like an alt or gen it fills the first batt then spills over to fill the second, and if 4 batts so on and so on , SOOO the last batt usually is a lazy batt in time , more so in a 4 batt configuration for sure, a 12 volt on each batt is just that, it fills each batt full, all batts should be cleaned and charged individually once a year at least , if using a 24 volt, but pulled and cleaned anyway once a year for any set up... , crud robs juice too,
 

greg burns

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AZ:
The battery tender brand makes a model with two separate 12 volt chargers in a single housing. I used one with my deuce that was stored all winter. The truck started right up this spring. I unhooked the battery cables and the dog bone before connecting the chargers. It only took a couple minutes to connect it all back together.
 

rrrr

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AZ:
The battery tender brand makes a model with two separate 12 volt chargers in a single housing. I used one with my deuce that was stored all winter. The truck started right up this spring. I unhooked the battery cables and the dog bone before connecting the chargers. It only took a couple minutes to connect it all back together.

I've got the same tender. I also disconnect the line between the two batterys and charge away. This is only if I'm not going to start/drive the truck for an extended time period perhaps a month. It only takes about 5 minutes and leaves me with a good piece of mind to know that they are ready to go.
 

glcaines

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I don't know if it really helps or not, but when I remove my batteries for cleaning, I always install the batteries in the alternate position. I have had zero problems with the U6TLs that came in my M35A2 and M35A3 trucks. I don't use a bettery tender on either, but the A3 came with a solargizer installed. I never let either truck go more than a month without being driven so my batteries are always up.
 

emr

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Yes rotating batts is the right thing to do also, Yes pulling batts and cleaning and rotating them will help one get the longest life out of them, so, I like i said, if the charger is a 24 volt they should be taken out and cleaned and charged individually to a full charge then rotated and put back in, if they have individual 12 volt chargers they should still be cleaned and rotated as said above, I left that out accidentally in this post but have said it 20 times in other battery threads, there must be a guzzillion by now. :) hey know one is making anybody do any preventative maintenance , but the things to do are listed, also if one takes short trips and the trucks batts are so big they keep starting her, well if they are never brought up to full charge regularly they are sulfating and will cut there life in half, I get a kick out of guys who say "My batts only lasted 4 years, I have 10 and counting on one set. hey dont worry , all this maintenance stuff is for the birds... :) Just kidden around, but batts are expensive, and they need care just like every other part on these trucks.
 

JasonS

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Yes rotating batts is the right thing to do also, Yes pulling batts and cleaning and rotating them will help one get the longest life out of them, so, I like i said, if the charger is a 24 volt they should be taken out and cleaned and charged individually to a full charge then rotated and put back in, if they have individual 12 volt chargers they should still be cleaned and rotated as said above.
There is no benefit to rotating the batteries; top to bottom, right to left, etc.
Each receives the same charge.
 

bassetdeuce

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Orange City, FL
Float/maintenance charging is fine, but I do like a proper full charge put on the battery first. Before a maintanance float, check the water, then bulk charge at high amp charge rate. Then switch to low charge to get through most of the acceptance "top off" phase. Do this with a good MANUAL charger and some monitoring with a voltmeter, and ammeter. I like to to this with the caps open to check the bubbling. As far as battery rotating, I dunno. Couldn't hurt I guess, except for your back.
 

steelypip

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Rotating makes no difference at all. Consider the circuit diagram symbol for a battery (below).

Note that all the cells (nominal 2.0 volts) are in a string together. Our pictured example is a 10 Volt battery if we assume those are lead-acid cells.

Because they're in a string together, if a current passes through one cell, the same amount of current passes through all the cells. There's no difference between the first and last cells in a string as far as current availability is concerned.

Chances are good that the cells do not charge and discharge identically. When charging, it is important to charge the battery until the most discharged cell is fully charged. The 'right' way to do this is to measure the specific gravity of each cell with a hydrometer during charging, and when the lowest cell reports a 'fully charged' specific gravity, you're done. It's a pain, and almost nobody does it.

The good news is that flooded lead-acid cells tolerate a mild overcharge very well. So SOP for decades has been to 'float' the battery slightly above the full charge voltage, and accept that a little electrolyte will be hydrolyzed ('boiled off') from the fully charged cells while the lowest cell is brought up to full charge. As long as you ramp the current down to something below about c/20, this method works well.

All constant voltage charging circuits work on this principle - full charge static voltage on a 12 cell string should be about 25.5 volts. Applying an extra 1-2 volts across the string still only amounts to a difference of 0.15 volts/cell, which means a very small amount of current. This is what is meant by the term 'float charging' - the string 'floats' at some voltage above its full charge voltage all the time. This works great in vehicles, which tend to be shut off for a minimum of 8-12 hours at a time.

The downside is that the string is always hydrolyzing a little electrolyte whenever the battery is fully charged and the charging system is working, which (along with high underhood temperatures) results in the requirement for a periodic topping-up of the cells with deionized water to replenish lost electrolyte. This is also one reason why batteries in 100% duty cycle installations tend to have much more elaborate charge control programs than the simple constant voltage system used on vehicles. 'Battery Tender' type chargers also have more elaborate charge programming, which is one reason that they can make even a puny motorcycle battery last forever.

So skip rotating the batteries in the string and, if you're feeling like you have to do something, pop the caps and check the fluid level and specific gravity of the cells.
 

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