I recently purchased 2 6 volt batteries from Costco for my travel trailer and wired them in series. I used them for 2 trips and when I picked up my trailer last weekend found that both were dead (I forgot to unplug the negative battery lead and accidentally left a light on the travel trailer for a few weeks). When I got home I attempted to charge the batteries and got the 'Dead' message on my Schumacher charger. I next attempted to charge each battery individually but my charger did not even recognize and try to charge one of the batteries and the other battery read 'Dead' after 10 minutes of charging. Do you think I received 2 bad batteries from costco? I tried using a different battery charger and have run into the same issues with the batteries.

I would say that running the batteries completely dead was the fatal mistake. Deep cycle batteries are designed to not be discharged below about 50%.

Lead acid batteries do not appreciate zero voltage. They are most likely permanently damaged even if you were able to exert some charge into them.

Most often when a deep cycle battery gets discharged below 50% charge (apprx 12.0VDC) and do not get re-charged back up right away they will start self destruct inside the battery...You need to have a multimeter reading the battery terminals when you are charging as also sometime when a battery is really low the battery charger will kick off and not keep appling DC charging voltages. Sometimes this has happened to me and I had to start out with a lower charging setting (like maybe 2AMPS) and sort of work my way up in small steps to keep the charger from kicking off.A couple of weeks of trailer lights left turned ON is probably a death warrant for your two 6V batteries. When all re-chargiing fails of course take them back and maybe you can work out a replacement deal with costco. They sell alot of Golf Cart batteries... I don't believe they are at fault however based on your failure description.Try lower charging setting and use a multimeter across the battery terminals and make sure it stays in charge mode for a couple of hours and hopefully the batteries will start returning to normal... I don't know anything about our brnd of charger but it would probably work better if you could each 6V battery separately. DO NOT however apply 12VDC to the 6VDC battery terminals. I think about 7.5VDC is the norm charging voltage... Like they always told me at work when I did something like this... "Bend over Braddy" and then each fellow technician gets a free boot shot...Let us all know how you making out... Those GC2 Golf Cart batteries are built to withstand alot of punishment... Roy Ken

Try using an inexpensive dumb charger from HF at 2Amps for a loong time. You may get lucky.

Died... but not of natural causes or defect. Costco may give you a pass but consider some solar to keep them charged. At least a battery switch to make the disconnect a bit easier.

Costco 6 volt batteries- both died | Good Sam Community

wa8yxm
Explorer III
Jul 23, 2013
You need to start with a "Dumb" Charger for a few hours, then go to the smart charger.. That can be an issue with smart chargers.
SkiMore
Explorer
Jul 23, 2013
I don't think it is nice to try to return them to Costco if he killed them due to his mistake. It isn't like they were defective.
Hoppypoppy
Explorer
Jul 23, 2013
Just to hitchhike on this topic....I am needing to replace my 6 volt batts. What do they run at Costco? (it's late, and I am too lazy to search right now.:D
msmith1199
Explorer II
Jul 23, 2013
I don't know if Costco does something different with batteries, but generally they take things like this back with no questions asked and give you new ones.
Pauljdav
Explorer
Jul 23, 2013
sh410 wrote:
Try using an inexpensive dumb charger from HF at 2Amps for a loong time. You may get lucky.

x2 this will work
JiminDenver
Explorer II
Jul 23, 2013
I have a customer with a hybrid he doesn't drive and the starting battery is dead every time it has to be moved. Usually I use a basic 2/12/75 amp charger but last time he bought a fancy digital model and it wouldn't charge the dead battery.
That battery gets drained over and over and still takes and holds a charge until the alarm drains it again. it's fine if started once a week or so.
Matt_Colie
Explorer II
Jul 23, 2013
DuPont (Is that you Heri?)

You have gotten mostly good advice to get started at recharging the bank, but I have some very specific experience you will be glad to hear. Real Deep Cycle batteries being what they are, they may well survive this ordeal if not left dead for very long and not frozen. Expect that once you have used the above tricks into fooling the good charger to do its job, that the bank may well come back to 80% of capacity. This is just because real deep cycle batteries were made with the expectation that they might be abused.

Good Luck

Matt
Gale_Hawkins
Explorer
Jul 22, 2013
popeyemth wrote:
sh410 wrote:
Try using an inexpensive dumb charger from HF at 2Amps for a loong time. You may get lucky.

X2 your charger is not reading enough voltage to activate the "smart " circuits to identify polarity and or if its a 6 or a12 volt batt.
Sometimes if you use jumper cables to parallel a charged batt you can get enough charge into a dead batt to get the charger going.
Good Luck, Mike

For sure.

I have done this more than once so I keep a 6/12 volt 2/6 amp manual charger since the "smart chargers" can go dumb on dead batteries. :)

Running a battery down and it setting for a while is not IDEAL but seldom is the end of the road for otherwise healthy batteries I have found over the years.

Let us know how it goes. If you have a set of jumper cables but no manual charger ($30 at Tractor Supply) you can trick your smart charger to working with the jumper cables letting the charge see the 12v from the jumping battery. There is no reason to have the engine running to do this. After the charger starts charging for a couple minutes you should be able to remove the jumper cables it it keep working.
bighatnohorse
Explorer II
Jul 22, 2013
Google: revive dead battery
Also search YouTube
popeyemth
Explorer
Jul 22, 2013
sh410 wrote:
Try using an inexpensive dumb charger from HF at 2Amps for a loong time. You may get lucky.

X2 your charger is not reading enough voltage to activate the "smart " circuits to identify polarity and or if its a 6 or a12 volt batt.
Sometimes if you use jumper cables to parallel a charged batt you can get enough charge into a dead batt to get the charger going.
Good Luck, Mike