windhund116

Who knows what voltage the tender is programmed to indicate as a "full charge?" However, it can't determine the reserve capacity. So, the voltage may be 12.2VDC, but once you try to start the engine, the battery's voltage may drop well below 12VDC.

Once you get the new battery, measure the voltage across its terminals to ensure the alternator works appropriately.

B serious

The pop is probably just the starter disengaging.

I wouldn't worry about it. Grab a new battery from Costco or Honda. Toss it in and give it a go.

twohoos

A tender can't charge a dead battery.

Some tenders show green/full when the trickle charge current reduces to near zero, which is what happens when a healthy battery is full. Unfortunately it also happens when a dead battery can't take any charging current.

Car Analogy

To prevent spark if leads touch, Tender won't charge unless it reads some minimum voltage. So it knows its hooked up to a battery.

To trick my Tender into charging when battery is below that threshold, I just use a 9v battery. Like from a smoke detector. I bought a 9v connector with long, bare leads. Then bought a pair of battery alligator clips. Not as huge as jumper cables, just something barely big enough to clamp to posts.

Crimped the 9v wires to clips. Had to strip extra length, and fold bare end over a few times to have enough meat for crimp to grab.

I hook up the 9v at same time I hook up Tender. Once it starts charging, I remove 9v. Tender will keep charging.

If battery was that low, its never going to have same capacity as before. But can still get years out of it.