Another Battery Question

[kearlms]

I have two 6-volt batteries for my TT and sense it is winter I have them in the shop. I have hooked them up to my battery tender in series to get the 12 volts. When I connect the tender up to the batteries the one that has the positive connection starts to boil almost immediately. Is this normal or is there an issue? I haven't noticed any boiling from the second battery, that the negative side of the tender, is connected to.

[kearlms]

So here is what has happened with the batteries. I put them on another trickle charger and it finally came up and said they were full. I disconnected and let it sit for 24 hours then tested with a hydrometer. One battery says full and the other is at 75%. I think I have a bad battery. So come spring I will be buying two new batteries for the TT.

[Lynnmor]

My bet is that one or both batteries are toast. Excess "boiling" is a sign of a defective battery.

[kearlms]

So I swapped the connections and it is still bubbling a bit. Not as bad as before. I also checked the voltage and they are at 6.4 volts each. I have also noticed that on one of the positive battery posts there is green corrosion that is building up. I cleaned them off last week when I pulled them from the trailer, but it is back. This is on the one that was boiling first.

[tenbear]

As beemerphile1 asked, what is the voltage on each battery?

[kearlms]

RJCorazza wrote:
Don't take offense, but are you certain the batteries are properly connected for series? Connect positive of one battery to negative of 2nd, then charger on positive of one, negative on the other.

This is how they are connected. I double checked. I am going out now to swop it around and see if the other battery will boil with the pos connected to it.

[time2roll]

I would call it normal for 48 hours. Although what was the voltage at the terminals where you connected? 6v? 11v? 12.6v? If 12.6 I would not worry for a few days at least.

[RJCorazza]

Don't take offense, but are you certain the batteries are properly connected for series? Connect positive of one battery to negative of 2nd, then charger on positive of one, negative on the other.

[hawkeye-08]

When we bought our used trailer, the car lot had a battery charger running on the batteries (2 6V). they had it hooked up wrong (across one 6V) and one battery was certainly warmer than the other. Once hooked up correctly, all was good.

[beemerphile1]

If you are boiling a battery with a Deltran Battery Tender, something serious is wrong! What are the voltage readings?

[kearlms]

When I get a chance I will go swop them around and see if the other battery boils also.

[2oldman]

If the batteries are sitting at about 6.4V, you really don't need them on a constant charge.

But something does sound wrong with one of them.

[Dakota98]

2oldman wrote:
Sounds like it's time for a hydrometer.

X 2 And the "Tender" is boiling the battery ? :h

[2oldman]

Sounds like it's time for a hydrometer.

[All_I_could_aff]

I have never used a tender on two 6 V in the manner you are but out of curiosity I would try switching the two batteries and see if they other one boils in the same situation with the positive on it and the negative on the other one