I've got 2 Group 65 Diehard Platinum batteries in my Excursion, and use an Odyssey OMAX-25A-1B to charge them. My question: Is there anything special about either the batteries or the charger that would make charging both batteries at the same time a bad idea?

For those of you who don't use Odyssey/Diehard Platinum batteries, I know the batteries are connected in parallel, and can normally be charged together. Odyssey/DP batteries require a slightly different charging profile, so my question pertains to them, specifically.

Mark

 

If it's a paralell system they should always be charged in paralell if you want them to last. Think of them as a matched pair.

You bring up a good point, different battery technologies have slightly different charging profiles. It's important to meet that specification, better a good charger with a cheap battery than the other way around. A few tenths of a volt doesn't sound like much but it is on a percentage basis. Given the expense of a few rounds of dual battery/alternator/battery replacements it pays to maintain the things. Found this website really helpful at getting a handle on good maintenance: http://www.batteryfaq.org

 

Times two!

Pop

 

I dont remember seeing anything negative about charging together in parallel when I read all the literature,I charge both pairs of Oddysey's that way in truck in signature & camper,there was mention about min/max voltage while charging.

 

What charger do you use?

Mark

 

the charge wizard built into the camper was within the specs by Odessey,the truck I keeped topped off with a Deltran Battery Tender waterproof 800milliamp,if it was run down much ,I would use My Solar 2/10 amp automatic charger I checked when charging a friends lead acid battery that was run way down & the Solar stayed within Odessey voltage specs.

 

The battery doesn't care what charger you use at one level. You can charge a 1500 ah battery with 15 ma wall-wart if you want, it just might take a few months. There are some limitations on the high side, but most people don't own those types of chargers.

Once two batteries are paralleled (or seriesed) electrically speaking you have ONE battery and should always be charged as such. There's no way around that.

 

not to intrude BUT your charge current has to exceed the steady state drain on the battery. +300 ma for us. 80 ma for batteries sitting unconnected on the floor.

cant go much above 14.2 because agm wont outgas for very long

 

This page has the Odyssey charge profile, and on that page you'll you'll find this graph:



From the OMAX-25A-1B manual:

In the first step, called the bulk phase, the battery is charged at up to the nominal charge rate (6, 12, 25, 40 or 50 amps) until the voltage reaches about 14.7V. The charger then switches to the second step, called the absorption phase.
In this step the charger continues to charge the battery at about 14.7V until either the charge current drops to 100 milliamps or the charger has been in the absorption phase for 4 hours, whichever occurs first.
The charger then enters into the trickle charge phase at 13.5-13.8V. The battery can be left connected to the charger indefinitely.

My concern, and the reason for this post, is that it seems to me that charging two batteries on a 25a charger meant for charging one would elongate the charging cycle. If the absorption phase times out early what happens? It doesn't sound like anyone here knows for sure.

Mark

 

Yes. What I was trying to get across was charging parallel doesn't change anything per se. It's simply a bigger battery. But the charger does need to be "sized" relative to the Ah rating. I tend to use an old school charger for bulk charging all the way up and let them cook for a little while. The Tenders used JUST for float.

If I had dual battery setup, esp. when using high quality AGM like the Odyssy would want to make sure to move some serious current through those things when charging, tho no more than 25% of the Ah rating of the setup. With a dual battery setup that's a big charger. No Tender is going to do that. Also and this is important, follow the absorption charge voltage, _adjusting for temperature_ over several hours.

Everybodies eyes bug out when they see 15 or 16 volts indicated but these are correct voltages _depending on the temperature_ Every cell will be on the same sheet of music after that, and THEN put it on a tender.

I'm figuring a lot of the problems that seem to be associated with dual battery setups can be avoided if a properly sized outboard charger is used periodically and charge profile observed. The vehicle charging system should be a lot happier too.

 

Though I don't own a camper, I can see the need to charge those batteries on a regular basis. As for the batteries in the truck, why would you need to charge them? I find that when they start running low, they are old and need to be replaced. Do your trucks sit for extended periods of time causing the batteries to loose power?

 

Looking at Odssey owners manual,it shows a picture of two batteries in parallel with no special instruction,.But it notes to check that your charger stays in range of 14.1-14.7 volts and not to exceed 15.0 volts or will cause pressure valves to open & out-gas.to answer your question,Im not a expert but have cared for a fleet of batteries for 35 years and I never heard of a charger that times out because a second battery in parallel, the battery charger senses voltage to trigger time out/float regardless if how many batteries are in parallel.also a note these little battery tender or two amp chargers wont be any good if batteries are deeply discharged,My 31-pc2150 Odyssey camper batteries will take a min. of 40 amps with a range of 14.1-14.7 volts to properly charge,which the charge wizard in our camper meets them specs.

 

Batteries self discharge just sitting there, and modern vehicles have a built in drain, with clocks, security systems and golly knows what else. Coupled with short trips, they tend to spend a lot of time in a less than charged state. That in turn causes sulfation and reduced capacity.

Batteries "like" to spend time in a fully charged state, this is where outboard charging comes in. Batteries also benefit from periodic equalization charges, a specific overcharge that tends to normalize voltages between the cells.

The idea here is to maximize performance and service life of a pretty spendy arrangement. Dual batteries should always be replaced in pairs. And weak, sulfated chronically undercharged batteries have gotta be tough on the charging system - not cheap either. See where I'm going with that?

 

I see what you're saying. My work trucks get a lot of miles on them, but my personal vehicle does get some short trips. Even though it gets driven weekly, it would still be a good idea to hook the charger up to it on occasion.