I think we're gonna need more details than what you provided.
I'm guessing that you are using a universal AC adapter and are trying to power up your recharging unit with it. There are a couple things that I can think of right away that could affect the functionality of the charging device. Check the actual charger to see if it lists what its power requirements are. If not, here is what I see as problems.
First is what you mentioned, the voltage. Second is the amperage. For example, I'm looking at my battery charger for the Canon EOS 10D and it says 8.4V DC 1.2A while the battery only reads 7.4V 1100mAh. My cellphone charger says 6.25V 350mAh while the battery only lists the voltage and 3.25V.
So the short answer is, there's really no way to tell what kind of voltage let alone amps you should be putting to that charger in order to make it work correctly if it doesn't say on the charging unit itself.
If it was me, I'd check eBay for recharging units. They are rather inexpensive there for these type of things.