It is possible to use 3400/Kanga Li-Ion batteries with a 5300; you just can't recharge them in a 5300 unless, as iamdigitalman mentioned, you are running System 7.5.2. I have personally run a 5300 from such a battery for several hours (amazing the run-time you can get), but as the 5300 can't recharge the battery, it proves to be rather impractical for everyday use.

Peace,

Drew