I have a trimmer Challenge sh-18v400 and couldn't find a 23V adaptor. In the end I decided to buy a 24V adaptor (lots of them available on eBay) and tried it. This works fine for me.
Make sure that:
1. the adaptor is at least 400mA (I bought one that was 1A=1000mA)
2. you don't overcharge. My batterypack states 1200mAh which means that with 400mA it takes 3 hours; so I don't charge the batterypack for longer than 3 hours. Otherwise this will likely effect the charge the batterypack is able to hold and could cause an explosion.
I hope this works for you too.
Steppefox, October 2010
