Any battery knowledge to share here?

Can battery tenders do more harm than good? Like, the cheap $5.99 ones from Harbor Freight?

I had all my batteries on these tenders (DieHard, Exide and NAPA, plus two 'vintage style' yellow-caps) this winter. They were inside my basement workshop, vented to the outside. Just for my own info, I checked voltage randomly over the months (typically 13.70 - 13.99V), and occasionally took them off the tenders for a week to see how the voltage would stabilize (typically 12.50 to 12.80v).

In middle of March, I noticed two of the 'no-maintenance' types wept some battery acid out of their top lids.

I cleaned it up, then:

- I took one of these off the tender and let it sit. It held 12.66v. I stuck it back in its car, fired up and it seems to work fine.

- I left the other one on the tender and used it in the 67 Satellite yesterday... It measured a healthy 12.56V when taken off the tender. I stuck it in the Satellite and it cranked poorly with no start. That's not usual for this battery.

So I shot some starter gas in the carb, then it fired. It ran well and the D/C gauge showed a good charge, so I took it for an hour drive. I stopped to enjoy the view. Went back to the car.. again it cranked poorly on start-up and then died. So I had to get a jump from a friendly passersby. Then it fired. I looked but didn't really notice any more acid weeping out of the top.

Again, the D/C gauge showed a good charge that stabilized and I drove it an hour back. I parked the car in my storage garage, took the offending Exide no-maintenance battery out and brought it home. Left it on my bench. This morning it measures a healthy 12.75V.

I'll take it to the Satellite and see how it cranks this morning, but in the meantime, -

- any advice as to what's going on with the no-maint batteries?

I didn't think they'd weep anything out the top, that seems like a bad thing.

Maybe this, or both batteries have reached its service life?
Did the constant low-amp 13.9 charge cook off some battery acid?

I just don't want to harm my batteries.

Thanks,
- Art

65 Satellite hardtop 361/4bbl console 727 2.76
67 Satellite convert 383/2bbl column 727 3.23
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