A bigger charger doesn't mean you will get a better charge. In fact, a trickle charge is better than a high current to recharge your battery - it just takes longer. If your battery tender has a 1.0 to 2.0 amp charge that is a good feed - just make sure you charge for more than a few hours. Your battery, at room temperature, should read roughly 12.5 volts at full charge. Anything less than 12.0 volts - you should replace the battery. Having said that, a real test of the batteries' worth is, after reaching full charge, do a load test which will let you know if the cold cranking amps (required for starting the vehicle) stays strong, even after a large draw of juice. You can buy a simple battery load tester for around $20.00. I think it's a great investment. A simple (not a fancy) voltmeter will run you at $10.00. Another great investment.
The beauty of having the voltmeter is that you can also make sure the alternator is putting out the required juice to recharge and maintain your battery while running. Even though your gauges should show the current running to your battery at 14.0 volts (roughly) I like to do a test right at the alterator posts to be sure (and a little more accurate). 13.6 volts or higher is good.
