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.

cosmomiller

I have a spare RV Deep cycle battery I use for my electric fish motor and I have used that to force a charge on a battery to get it up to the point where the charger recognizes a battery and charges. Does not take long. Never thought of a 9V.

twohoos

Yes, but in that case the tender won't indicate green/full, it will indicate a disconnect or fault. OP stated his tender was reading green/full when the battery was fully dead (no interior lights, dash dead). That's caused by a bad design that assumes when charge current drops near zero it means a full charge is complete. But when you disconnect and reconnect it, it resets, applies a full trickle charge, and goes back to indicating charging. That's what the OP observed, and that's what confused him into thinking the problem was something other than just a dead battery.

Not all tenders do this. Even for the ones that do, it most commonly occurs when the car sits for several weeks/months. If the battery is marginal at the start, the tender can achieve an "acceptably" full charge and start indicating green. But then as the battery goes through its last gasps and its voltage degrades, the tender just continues happily showing green. It's only when you disconnect/reconnect that you discover the battery is long since gone.

My car routinely sits for weeks/months at a time, so I'm well acquainted with the quirks of tender behavior.

engifineer

Battery terminals clean? Remove leads, clean with a battery terminal cleaner, put them back on and make sure. A very poorly connecting batt terminal will still be fine under low load but will basically blow the tiny connection it has under higher load (like trying to start the car). And that will create a pop, or sparking noise sometimes. This is THE main way at dirty battery terminal will start showing up. That tiny part that is still making good contact basically acts like a "fuse" that blows when more current is passed through it.

Could also be that there is another bad connection on the main power or ground (like the main batt ground to the chassis). The tender would still charge the battery just fine in that case but it would appear dead when trying to start the car.

Battery could still be it but check those items first