Battery is NI-MH 6.0 V 1400 mAh
Charging for 1 hour with a 300mA charger will put around 300/1.4 = 214mAh
on the battery (max.) - not much.
This is IF you are using a proper charge circuit - I'm not sure you are, since you just called it a "300 ma 6 vdc transformer".
What exactly are you using to charge the battery (full circuit please)?
Let's start with that, since if you use something wrong, you can ruin your battery pretty quickly.
NiMH cells are nominal 1.2V and has a charge termination voltage (V_ct) of 1.40V to 1.45V.
6V means that it must be a 5-cell battery, which then needs a V_ct of 7.0V to 7.25V
- can your charger reach that voltage (plus any voltage drops in your circuit and contact points?
If not, it won't even get the 214mAh aboard.