I found this replacement Makita BL1850 Battery
* Type: Li-ion
* Volt: 18V
* Capacity: 5000mAh
* Color: Black
* Weight: 728.22g
* Dimension: 114.80 x 74.55 x 65.20mm
The more about this battery you can see on http://www.drill-battery.net.au/buybatteries.php/makita_BL1850_power+tool+battery.html