Had a similar experience with Deltran on their Battery Tender Plus.
I kept all of the original packaging, including the big, bold "10 year warranty" on the packaging and the warranty sheet itself.
No where did it say there were any fees at that time (not sure if they changed their warranty sheet since or not...they claimed they were going to change it after I filed a complaint with the Better Business Bureau)
When I called for an RMA under warranty, I was informed that there was a $12.95 WESH (Warranty Evaluation/Shipping Handling) fee, plus you have to pay to ship it to them.
I protested that the WESH fee was not disclosed on the packaging or on my warranty sheet and their response was "it's right there"....I said "where?" and they referred me to the web url
www.batterytender.com that was in the footer of the warranty sheet.
Including the shipping cost to send it to them, it would have been over $20 to get it repaired under warranty...you can buy new/delivered for $40-$47.95.