Battery charger.
Like Nigel said, the charging method depends of the battery type (chemicals). Charging the Li-ion batteries, at the end (4,2V/cell) the charging current must be cut off. In other case the battery may explode. At the end of charging the Ni-Cd or Ni-Mh batteries, you can use the trickle charging methods. The trickle charge current must be C/25…C/50 (C=capacity in Ah). I think that you are using an SLA battery. The SLA battery’s cell voltage is 2V, then you have 3 cells serial connected 2*3=6V. The SLA battery must be charged with constant voltage and charge current limit. The maximum current is C/10, so you can’t use a rapid charger. The maximum voltage limit is 7,2V (2,4V/cell). You can use a 7,2V power supply with C/10 current limit as a charger. The current will drop down at the end of charge. You can live the battery on the charger.
I am familiar with a lot of batteries types and chargers. I will send a simple charger schematics for your battery, if you send me the battery type. What does it mean: "Transfarmer- 9-0-9 Volts" ?