Be careful if you charge them at too high a current, then they may overheat and explode.....but at 200mA or less you should be ok.
You could always just buy a current source rated 200mA or less and connect that to it...check that it goes up to 30VDC. Preferably one with a voltage cut off at 35degc, no higher.
But really you should remember to only switch the current source on after you have connected it to the battery.
-Becuase current sources on open circuit tend to shoot up in voltage, and then if you connect it to the battery, it will be big inrush etc.
LED drivers are current sources , so that may do the job for you.