I do recall how originally the 5300 series was gunna have Li-Ion batteries, but due to one exploding during testing, it was swapped out for a more traditional NiMH battery.
However, the 3400 did ship with a Li-Ion battery, and in the same form factor as the 5300 style battery. So, is it possible to try and use one of the higher powered 3400 batteries in a 5300?