iwan wrote:my roomba charger died....after about a month i bought me a new one. a universal one that delivers 24V and 750mAh. I have read on this forum that this would be a good charger.
The Roomba charger output has 22.5V and 1.25A.
The 750mA is not the problem as long as it can supply more than 400mA.
The 24V output may put load on the internal charging circuit.
when i measurd it after an hour on the charger it was around 15V ( while the battery is 14.4V)
i did not do a load test on this battery.
The no load terminal voltage should be around 17V after charging.
Your battery is not being charged. It may due to your universal charger.
If your universal charger is not the switching power supply type, when Roomba is drawing 1.2 - 1.3A, the output voltage of your 0.75A universal charger will drop to the level below the Roomba charging requirement. This may be the reason why you are seeing only 15V no load battery voltage.