LITHIUM BATTERY

I have a HPT435BT radio that is set to 25 watts. I use a large marine deep cycle lead acid battery to power the radio. My 85 year old body is having a hard time lifting the battery. I am considering buying a 12.8 volt 20 amp hour trolling motor battery. If 25 watts / 12 volts = 2 amps +- * 1 hour - 2 amp hours and I only work 5 hours per day, that would be 10 amp hours. Has any one tested this out? I love to survey a few hours a day a few days a month. What kind of battery charger do I need?
 
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