Negative battery terminal HOT

[SV Pretty Lady]

I have 3 new Renogy 100ah gel batteries. Had them on a new Xantrex charger, but the charger quit after a week. In the meantime, I bought a cheaper charger while waiting for Xantrex to do whatever they do to returned battery chargers.

Two of the batteries negative terminals spark when hooked up and get really hot when the nut is finally tightened. The other battery is fine. No problems. Why is this happening? Is there a mis-wire somewhere along the line? Or are the two batteries bad?

Everything is unhooked right now while I figure this out. Thanks for any help.

[Ron Hill]

SV : You have a shorted circuit in your wiring!!!  You'd better have your wiring circuitry checked before attaching your new rebuilt charger or your batteries wiring backup!!
Have the new Batteries checked just to make sure that one doesn't have a dead cell!!

A few thoughts

[J_Sail]

You might have a wiring error, or you might have one or more batteries with shorted cells from old age.  Check the open-circuit voltage of each battery with it fully disconnected.  If one or more of them is significantly lower than the others, then that battery might have a shorted cell, which could produce your symptoms. A shorted cell will reduce the output voltage by 1.2v. 

(A discharged battery may also show a low voltage, but that would have been resolved after sitting on your charger, and with all the batteries in parallel on your previous charger, they should all be at the same state of charge absent things like shorted cells.)


Ideally also check each one with a modest load across it (a few amps), but finding a good device to load it can be challenging.  I own an inexpensive commercial 12v battery tester, which can apply loads of up to 100amp, but I also use a 6 ohm 50-watt resistor that I bought somewhere decades ago. That draws on the order of 2 amps, depending on actual battery voltage.

[KWKloeber]

SV,

I recall one of RC's aka mainesail aka Rod Collins aka Compass Marine's articles was re: adverting a meltdown on a battery post due to (? CRS 😳). Might check it out?

Tho, I've been the shorted cell route (wet cells) and it seems the most likely cause. She would bubble hot electrolyte out the cap.


An aside; ignore unless you're bored —

In my situation the grp 31 (tho showing dead) did not come up w/a fault/needs replacing on WallyWorlds super analyzer (not the hand-held garbage one.) No luck, no replacement under warranty.

I bought a bead tester, showed the asst tire/auto mngr the dead cell. No luck, no repacement.

Witnessed the dead cell with the auto tech, who agreed it needed to be replaced.

Asst store mngr called in, I explained the situation, and auto tech confirmed it.  No luck, no replacement. "If it doesn't show on the box, Wally won't replace it.  After explaining how battery cells can short (no profanity, I'm surprised) I was told to take my battery home.  "No," I said, "I'm not lugging that monster home and back, because tomorrow you WILL replace that battery."  At which point I was re invited to leave with or without my grp 31.

Needless to say, the next day they replaced it with a smile (it's handy to keep chain stores district manager phone numbers in your contacts.)

While chatting w/ the store manager a year afterward on a question (what is the remaining CCA & Reserve levels they use to determine a warranty replacement?) I mentioned the other battery and invitation from the asst mngr. "Oh, we promoted him from 'management' to 'customer' six months ago so he could see the other side of the fence more clearly." 
I have always termed it "reallocating the resource to the community."

-k