Tom from Optima's web site
6. Can you trickle charge an OPTIMA? Solar card charger?
Yes, you can use any charger on an OPTIMA as long as the voltage is regulated properly. If your charger will remain on indefinitely the voltage should be at 13.8 volts maximum with a one amp maximum current.
Web Page FAQhttp://www.optimabatteries.com/publish/optima/americas0/en/config/product_info/technology/faq.html#000100010006
Now from Battery Minder web page
Input 105-130 Vac 50/60 Hz
Output 12 volts @ 4.0 Amps
Charge Voltage 14.4 Vdc
Float Voltage 13.2 - 13.6 volts
Desulphation Pulse 4.0A @ 3.26 MHz
Float Current 5 mA - 1 Amp *
Size/Weight 4-3/4" L x 3-1/2" W x 3" H / 4 lbs.
So from all this I say it will not harm the battery, but calling Optima and asking them which charger they recommend is the best way to go. After all if they tell you xyz charger is the best and after using it the battery quits working then you can a case to have optima replace your battery, if you get just any battery charger and it fries the battery you are s.o.l.l.( that is sorry out of luck loser). Right now I an charging my blue top with a 5 watt solar charger thats only gets sun about 4-5 hrs a day and keeps the battery fully charged and ready to go. However since winter is coming I need to get another charger on it as the solar charger keeps my pool cover pump battery charged.