The excellent Battery Tender Jr. is available for around $23.00. You

can put four of them on a cheap power strip to charge a bank of

batteries and you will have spent less than $100.00 to properly charge

each bank of your batteries.

For even less you can get a similar small battery charger at Harbor Freight.
They are $10 but are often on sale with a coupon for less.

http://www.harborfreight.com/automat...ger-42292.html