[fox46]

Both the teams I mentor use these: http://www.tecmate.com/u_accumate_pro5.php

They are an affordable, compact and brain-dead solution to battery charging. We have them wired up to battery connectors so all you do is plug your batteries in and when the light turns green you're good to go. If you have five batteries which are always plugged into one of these and take them home at the end of the competition day to charge you should never be left without a battery. If for some reason you need to charge a battery at a higher rate, you can connect multiple terminals to one battery to boost the charge rate.

An important note about the batteries we use. The ONLY way to reliably test if a battery is indeed good is to use a load tester. This is a fancy voltmeter with a large resistor (heating element) inside it which loads the battery heavily to check that it is still capable of supplying sufficient voltage under heavy load. Last year Cybergnomes went to 6 motor drive and we found that the performance was extremely different between the new batteries that we had obtained that year vs the old ones. After load-testing them it was found that nearly half of the older batteries were incapable of supplying the same power as new when under load. The "failures" were attributed to storing the batteries at the end of the year and leaving them in a depleated state. With a lead acid battery it is very important to exercise it during the offseason. If you simply store it and forget it, the charge level can deplete. If these batteries are left in a depleted state they are prone to sulfation which is a formation of sulphides internally. These crystals can severely degrade the battery's performance. The best solution to avoid this problem is to charge your batteries or even better, cycle them (discharge, charge) regularily during the offseason. The phrase "use it or lose it" applies here. This type of failure can be very difficult to diagnose because the battery will test full voltage and without a loaded tester will show charged however, as soon as you apply a load the voltage nose-dives and you realize the battery can only store a fraction of what it should.