I'm no battery expert, but sticking 5v straight to a battery sounds quite dangerous to me!!!
For batteries that are unregulated (like the SD batteries) the charger unit for these has circuitary in them to measure the amount of charge going in and at what rate it is going in, and then when the battery is fully charged the circuit cuts off to stops charging, uncontrolled charging would probably cause the battery to heat up and vent
In a regulated battery (like the Tornado batteries) the circuitry is in the battery housing and serves the same function as above.
I would not mess with batteries, and if you are building mods, make sure there is a vent hole in the battery housing just in case the battery goes "hot" and gases out.
As I say, I'm not a battery expert.... but I'm sure one will be along to reiterate the dangers