Wiring batteries together for storage?

[Brybo86]

So I have 4 different batteries for my various 3 season toys. They are all 12 volt batteries. All of the batteries are in good voltage health and start their respective equipment well.
2 of them are 4 amp hour, one AGM and one flooded
1 is a 6 amp hour AGM
1 is a 12 amp hour flooded

Can I wire them all in parallel and connect them to a single battery tender/charger for storage this winter?

Is this going to hurt any of the batteries? I would not be using this battery "bank" to power anything, just simply used to keep them all charged during storage.

Is there a problem mixing different amp hour batteries?

If the above is all ok how small of a gauge wire could I get by with between batteries, I have some decent speaker wire that I could cut up to make the connections. I'd rather not go buy a bunch of terminals/connectors and bulk wire to make a couple feet of connecting cable.
Thanks in advance.

 

[Donald]

I would only try this on a float charger that says it can handle multiple batteries (BatteryMinder).

Their directions say as long as they are all flooded you can do 4 on one charger and 6 on another BatteryMinder charger. Interconnect with #18 wire.

All batteries should be fully charged and tested to be good before connecting them up.

I have done it in the past with 3 batteries.

 

[bullwinkle]

I do it on my deep cycles, but I've never tried it on different sized batteries.

 

[Donald]

BatteryMinder says different size batteries and deep cycle and starting OK, just not a flooded and AGM together.

 

[JHZR2]

Some will be undercharged or overcharged, depending upon the nature of the various batteries' impedances and health.

Id parallel two just for slower drawdown of some very small loads. Nothing sizeable as it could drive one battery into reversal.

Im less concerned with overcharge, because they are pretty well controlled on voltage and current, and these maintainers are pretty small. Still, the time at a high voltage could overcharge a small battery if the sizes of the two are too great, especially if one is in poor health and the other isnt. Once it hits float, it should stay floating. If the logic allows the battery to rest for a time, does a load/loss test and then recharges in the normal CC/CV manner (the Minder 2012 may do this), then Id be a bit more concerned than if it were a smart charger that just keeps it at one temp-dependent float voltage constantly...

 

[Voltmaster]

if all are same voltage ( standard lead acid ) you can put all of them in parralel and connect it to charger or whatever.

however if the Amphour is very diffrent , lets say the biggest one is twice the smallest, there is chance of too much current flow to small battery which may or may not destroy it.

A smart charger will keep the voltages low enough while monitoring current.

 

[440Magnum]

It will be OK as long as they are all the same battery chemistry (lead acid), and all batteries are in good condition.

The only risk, and its actually a risk anytime a battery is kept on a charger long-term, is that a cell in one battery could begin to fail and discharge all the other batteries until its electrolyte runs out because the battery with the lowest open circuit voltage will take most of the charge current. That could release a good bit of H2 gas, but then just charging batteries does that. Do this only in a well-ventilated area.

I'm not a big fan of "battery tenders" or other full-time chargers. Even the smart ones seem to get dumb from time to time. We've had computer UPS systems at my work fail to detect cells going bad, and continue to charge them until the AGM battery case puffs up and you can't slide the battery tray out. Twice we've been alerted by the sulfurous smell BEFORE the "bad battery detected" monitor goes off. And these are $5000 power systems, not $30 battery tenders :-(

 

[2cool]

The main issue is the types of construction of the batteries. AGM is charged at a different rate and voltage map than a flooded battery. Both are lead-acid chemistry, but because of the different construction, are charged differently. East Penn Mfg. has information about this on their website. I recommend one charger for each type, the .75A will do the job if the batteries are charged fully beforehand.

 

[Donald]

Also if you are going to float AGM, you should have a float/maintainer with a switch for flooded/AGM or a dedicated one for AGM.

 

[eljefino]

There are two different flooded lead acid chemistries, one is GM's maintenance free and one is the kind with the pop off tops. Calcium is in one IIRC. They need slightly different charging voltages. I wouldn't mix unlike ones.

 

[Donald]

Originally Posted By: eljefino
There are two different flooded lead acid chemistries, one is GM's maintenance free and one is the kind with the pop off tops. Calcium is in one IIRC. They need slightly different charging voltages. I wouldn't mix unlike ones.


What you say may well be true, but I have yet to see an AC charger that has a switch for that. Certainly GM could have done that in the voltage regulator for the vehicle.

 

[johnachak]

Originally Posted By: Donald
Originally Posted By: eljefino
There are two different flooded lead acid chemistries, one is GM's maintenance free and one is the kind with the pop off tops. Calcium is in one IIRC. They need slightly different charging voltages. I wouldn't mix unlike ones.


What you say may well be true, but I have yet to see an AC charger that has a switch for that. Certainly GM could have done that in the voltage regulator for the vehicle.


I believe almost all modern chargers (All of mine anyway) have a maintenance free setting as well as deep cycle.

 

[meep]

it will work. weaker batteries will pull the chain down but the float charge should keep them all healthy. note that a weak battery may warm up a little compared to the others, if so pull it out.

only other thought i have is of caution. I've considered doing this as well. If it were me, I would fuse every battery individually--- because if you short your leads at any point, you have X# of other batteries shorting through them---bad.



@440Magnum---- these wouldn't perhaps be symmetra UPSs with the SYBT2 packs, would they?

 

[SHOZ]

Different size cells will require different amperes. You will end up overcharging the small cells and under charging the larger ones.

With most AGMs their shelf life is a big plus. I would not bother keeping a float charger on them, but just charge them up before storage. I have a small AGM for my lawn mower. It only takes a 5 minute charge in the spring to bring it up to voltage.

 

[1 FMF]

you can connect all the batteries and have them wired together to be on a "float" charger to keep them all stored over 13 volts.
Only do this after you know each battery has been charged separately and is at or near 100% state of charge.

for wiring a float maintenance charge will be a couple amps at most so any wire that is 3 feet or less is going to work between the battery posts. the big thing is the more batteries in your group, the more amps a single float charger will need to output to keep the group over 13 volts. some float chargers only do 1 amp max so it's easy to exceed it and if you did you can easily tell with a volt meter, your float charge will be less than 13 on the bank of batteries. as long as the voltage is kept over 13 for storage, all batteries regardless of construction will be fine. just don't connect all the batteries together in parallel then expect to "charge" them properly. charging should be done individually on each battery.

 

[martinq]

Originally Posted By: SHOZ
Different size cells will require different amperes. You will end up overcharging the small cells and under charging the larger ones.

This is incorrect.


(Basically what 1FMF said above, but...)

You can parallel your batteries and their voltage will stabilize. The AGM needs a bit more voltage to fully charge and, if it's a good one, should easily handle being off of charge for a few months. (how long do you intend to store?)

Check the resting-voltage on each battery (off of load and charge for 12-24hrs) before you connect, they should be within 0.1v (AGM is likely higher). Wire the THREE flooded batteries in parallel but connect the charger to opposite corners.

+ve to batt1
-ve to batt3

Wire gauge isn't important as long as it's sized to your charger and all batteries are charged over 90%. Also be sure you are using a float/tender and not a regular charger. Check the voltage of the pack every few days to see how it's going. At 25C the voltage should settle under 13.5v unless your charger is temperature compensating, then it should increase as temperature drops.

http://en.wikipedia.org/wiki/Float_voltage

 

[eljefino]

Ideally one would unfasten the interconnects and measure each battery individually both immediately after disconnecting and after setting for a while to soak in the surface charge, so they could spot a bad battery.

With all this work, just get some individual Battery Tenders?

I don't even know where all these batteries are, sitting together. Do you pull them from cars? I guess down South if you put a battery in your cold basement it would preserve it better than being outside... but up here cold is great for slowing chemical reactions and preserving (charged) batteries.

 

[eljefino]

Originally Posted By: SHOZ
Different size cells will require different amperes. You will end up overcharging the small cells and under charging the larger ones.


Different internal impedances from battery to battery (and cell-to-cell within each battery!) will take different amounts of the available amperage. This will differ from year to year as batteries age and new ones get thrown into the mix. Assuming very even climate controls you might be able to spot this with an IR thermometer, but it'll only be a degree or two warmer if it's guzzling all two amps.

 

[Donald]

My batteries come from boat, Bobcat, 2 generators, lawn tractor

 

[dareo]

I'd only do it if they were all the exact same size batteries and close to the same ages. It might not cause any issues, but charging them one at a time is safer. the batteries will try to charge the lowest voltage in the bank, so if you must try this, keep it at a 2 amp charge so overcharging will be highly unlikely.