Thread: AGM Battery Carger Question

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I have a small AGM (absorbed glass mat - XSPower/Odyssey type) in the '33 and have a Battery Tender Plus hooked up to it. For the last couple of weeks or more the charger continues to show steady red, flashing green LED's which signifies >80% charge, but it never gets to steady green for fully charged. The car is currently in the unattached shop building which I only heat when I'm working, but the charger was doing the same thing in the attached garage, which stays 40+ due to heat loss from the house (25F outside now, 46F in the garage). Is this a normal winter time charger situation, or do I have a battery/charger problem?

I don't remember his screen name right now, but the XS guy signed on here awhile back when you ordered one of theirs didn't he? He'd probably be the best source for an accurate answer I would think (hope?).

Originally Posted by Bob Parmenter

I don't remember his screen name right now, but the XS guy signed on here awhile back when you ordered one of theirs didn't he? He'd probably be the best source for an accurate answer I would think (hope?).

Yeah Bob, that's Nathan@XS Power, and he's the guy I talked to when I bought my battery. I may have to give them a call, but thought someone else might be seeing the same thing in the cold temperatures.

I have a battery tender Jr on my 34 that's in the attached garage no heat. it stay's green all the time winter and summer unless it's driven then goes red for a bit when first hooked back up. the garage is insulated with insulated doors it get's heated when wife drives into the garage heat from her car. the battery is at-least four or five years old just an old standard battery. I do have a battery disconnect switch on it.

The charging action is different between a wet cell or gel type battery and the absorbed glass mat (AGM) battery. The wet/gel cell accepts the charge at a standard rate up to full charge, but the AGM rate of charge changes as it gets closer to full charge. I did hear from Nathan at XS Battery via e-mail since the forum was down this morning. He asked a couple of questions, and advised the following:

There are a few questions I have. Did it just start doing this and have you been charging it the same way all the time or did you change something? [Started about two weeks ago, nothing changed with the hookup. It did go to steady green (float mode) once, but after the next start has never done it again.]Is the battery hooked up in the car when you are trying to charge it? [Yes, the battery is in the car and hooked up.]

Sometimes with the Battery Tenders the cold weather can have an effect when trying to charge the battery. The Tender is such a low amperage that if the battery drops down in voltage much it may not be able to charge the battery fully. It can maintain the voltage for storage above 12.6V, but may not be able to top it off with a full charge.

The answer may be to start and run the car to boost the charge rate via the alternator for 1/2 hour or so. Weather does not support getting out for a drive right now

Mine does the same thing, Roger. And I have an attached garage with comparable temperatures.

Update - I went out to the unheated & unattached shop this morning and the Battery Tender is sitting steady green, indicating a full charge. I had not been out there for several days, and the temps have ranged single digits to above freezing. Looks like the charging rate is just a temperature thing.

This morning my charger went into a "not connected" indication (red flash) when I reconnected it to the battery leads, and as I messed with the charger wires leading to the clips it seemed that I had a broken wire. Did a quick continuity test from the downstream side of the in-line fuse to the aligator clip and sure enough I got infinity, but could get zero ohms with selective movement of the conductor. I had a few fuse holders in the wiring stash, so I changed it out. After a couple of hours it is still charging, (steady red, no green) which leads me to believe that I had a high resistance connection sometimes, and an occasional break in connection. This may have been a part of my winter time problems - time will tell...