That's what I am asking. I don't know enough about battery technology to know if it's worth the hassle to return the old one for a new one. I am hoping some of the battery brainiacs (and you know who you are!!) in here will be able to give a good answer of the pro's and con's.
I'm no
"brainiac" - but I play one on the bike forums....
I will offer these comments just as a "guess" - that's all just a guess about the "bad battery" situation.
I think this is a case of possibly defective or damaged battery-cell "protection-circuit" boards. And there is no way of knowing if the boards are manufactured poorly, installed poorly or are being damaged by transportation mishandling or user error.
But the end result is the possibility that they will fail to regulate voltage when charging the battery pack. In most cases, even if the board fails, the charger would still limit the voltage and current to the battery pack and you would simply have a hot, smelly mass melted battery cells beside your hot (but not on fire) charger.
However, the battery cells can contain irregular or uneven concentrations of electrolyte. (cell jelly) If there is enough of an "air bubble" (or gas) trapped in the cell as it continues to heat over a long period of time the result could be an explosion. Along with the "pop" - the material ejected could be hot enough to start a fire or burn you.
For anyone who knows how to use a multi-meter it is a rather simple process to measure both the current and voltage of battery and charger as long as you are willing to splice up your own cables to insert the meter in and across the charging circuit. If you take the time to observe the current decreasing as the voltage nears its cutoff point - you pretty well know all is well.
Fully discharged batter packs will draw between 1.5A and 2.1A for a few minutes.
Within five minutes any very high reading should have fallen to near 1.5A (if not you have a poor charger regulator)
You should be able to "watch" the current decrease at about 10mA per minute for the several hours. This means you would see about .9A an hour later.
Three hours later you would see a nearly fully charged battery, drawing somewhere around 20-30mA. If you check terminal voltage- it should be approaching 8.1-8.4V.
That is all.
But I don't know, this is just my best guess. In any case, I treat my batteries gently and do not let them get bumped or dropped.