It says right on the nameplate of your battery that max charge is 1.5 amps. Being that your battery has only a 5 amp hour capacity, I would not charge it at more than one half amp(500 milli-amp). If you go much over that, you will eventually build up heat at the top end of your rechrage cycle, which will reduce the efficiency of the charge, and also cause loss of battery capacity over a few cycles. At 500 ma, if you start from a completely discharged state, your battery will be fully charged in 10 hours. Be careful not to over charge, because batteries don't last as long when you do that, and only having 5 ah to start with, you don't want to lose very much capacity. You can find 500 ma trickle chargers with slip on connectors that will fit your battery.

I got a 7 ah battery and charger together from BassPro for $29.99 for running my sonar. The battery is not much bigger than the one you got, and fits nicely inside the tackle bag on my kickboat. You could return your battery to Radio Shack and order that set from BPS if you have trouble finding the charger. The battery and charger set at Bass Pro is listed as a power source for the Aqua-View camera system if you go to look for it. It is item number 38-521-007-00. The picture they show is not exactly what was sent when I ordered it. The battery was from a different manufacturer, and the charger had slip on connectors instead of the alligator clips they show on the website. I prefer the slip ons, because they provide a better contact(they were made for those terminal types) and they will not fall off if they get bumped.