Nudnik wrote:I wonder if a laptop power adapter would work. For example my HP adapter has 19 volt output,...
It is necessary to include the PSU's amperage (current) as part of such "wondering".
When substituting an alternate dc PSU to do Rommba 4XXX charging (i.e., charging current will pass through the robot's internal charging control circuit) it will be wise to emulate the characteristics of its Fast Charger, in the limit, as shown in this post:viewtopic.php?p=25609#p25609
You will prefer the current delivery capability to roll off at less than 1.3 amperes. Of course the PSU may invoke current limiting at lesser current levels, and the battery might reward you with more cycles. Charging at currents less than 1.25A,NOM will mean the process requires more time to complete -- so there is a trade there.
If you substitute a 19V, 3A PSU for Roomba's PSU, you stand the chance of ruining the robot's U2 & U4 MOSFET charging switches, since they will be dissipating more than twice the watts during the early phase of high-rate charging that they would if the Fast Charger was being used. Also, the low 19V level may not fully charge the battery because some of that voltage is lost within the controller before it reaches the battery terminal (the applied voltage would be around 17V, which means the battery would finish high-rate in the 15 to 16V range, but extended trickle charging might raise that to a normal level).