Is there any way these tenders can overcharge your battery? I just don't know if I should trust them or not.

 

I leave the wifes bike on a tender for weeks at a time. I have never had any issues in leaving a battery on a tender.

 

No overcharging with a "battery tender". It will only charge the battery once the level drops below a certain point......It's when you put the battery on a battery charger or trickle charger that it will continuously charge the battery and most definitely cook the battery.