OldIHC

I bought a 6 volt battery that I put in my truck last year and it began to fail so I took it back with warranty and got a new one for free it was working really good at first, but today when I went to turn the engine over it was clicking so I assumed that the battery must be dead, however, when I put it on the charger, the charger clicks on and off as if the battery were fully charged. Does anybody know what could 've causing my batteries to keep failing in the truck? I don't drive the truck by the way because I have not fixed it up enough for it to be safe drive yet.

Batteries are alive!
BTW, your post sounds just like "I've fallen and can't get up!"
Try another charger. Chinese junk has invaded our lives. Nothing better than a real USA battery charger. And NOT a trickle charger.
Six volt batteries don't exactly fly off the shelf. Hmmmm..Wonder why? Maybe you got two "past pull date" ones.
The "born on" date should be on your battery.
Today is March 10, 2018.
OR...it could be time to move into a new millenium with a 12v conversion...
Batteries drain and batteries lose capacity. The two appear the same...
Time and heat cause "sulphation". The battery plates get a coating that the funky electrons can't penetrate.
And yes, there are junk batteries.
But you are getting the "least chosen item on the menu". 6V. Don't EXPECT freshness.
I can hear any number of of my smart ex-bosses saying "maybe you should drive it more!".
I think the lead-acid car battery longevity record (in my experience) is about 8 or 10 years with MOST batteries giving up at 3-5 years. That's on a daily driven car. Those that sit all the time don't last nearly that long on average. Car batteries like to be discharged a bit and then immediately recharged as opposed to deep-cycle batteries than can be repeatedly run until dead and recharged indefinitely.
Once you get the thing started again check the charging system voltage. Fully charged 6V batteries come in at about 6.6v. Charging system voltage has to about 7v.

http://usbattery.com/wp-content/uploads ... odes-2.pdf

This stamp is also put into the battery case.

I don't think there is anything wrong with the battery charger or the battery itself, I was thinking is there something electrical that could be drain the battery as it sits?

If battery is fully charged and you get just clicking,

Clean up the connections at battery and starter/solenoid, reroute battery ground cable to starter mounting bolt, try starting it,

If it doesn't start now,

Jump with a known good battery or 12v. If it doesn't start now you have starter/solenoid/wiring issues,

My goodness...don't guess. It just makes us all look silly. Lead-acid battery behavior is well understood.
6V batteries and 6V charging systems are not exactly COMMON anymore, though. That was my point about going to 12v. "VAT 40/ VAT 45" battery and charging system testers are everywhere there's a real repair shop. I don't think they do 6v evaluations, though. Mine doesn't.
In that case a volt meter is your friend..WHAT is your battery's voltage at any given time?
Our old trucks have a definite battery connection problem. Run fresh battery cables all the way to their destination (run BOTH to the starter) and bypass any number of crappy connections in the frame, etc.
And then get back to us.

Ok thanks for all the advice and suggestions. I don't know how to do a 12 volt conversion nor do I have the money to, but I have cleaned all the connections and I did replace the positive cable. I couldn't find a negative cable that is long enough.

Any improvement?
6V stuff needs the thickest cables. Heaviest gauge. Counterintuitve. Expensive, I'm sure.
BOTH cables need to be replaced and / or extended for maximum benefit.

When someone says "I can't afford 12V" my eyes roll a bit.
THIS 6V stuff IS costing you money. Never mind the aggravation of being 6V in a 12V world.

I really don't have the money! I am 15! I don't know how to do all the things required for a conversion.