I suspect my POS battery tendered actually killed my RedTop, although there were to 'fingerprints' to positively ID the perpetrator, however it was after the over-the-winter trickle charge from that box that my negative battery post popped-out of the case, by the time I was ready to hit the road for the 1st car show I very much needed a new battery b/c that post literally detached!!!

Sooo....if it was the tenderer that did the battery in, by perhaps overcharging it, it was caused by junk equipment.

Prior to using that trickler charger I would remove the battery from the car and occasionally (once a month) charge it with the regular charge.

This is mid-west winter climate, right across the river from Detroit, MI.