I don't know how the Roomba charging circuitry is designed, but it's not at all unreasonable, particularly in consumer electronics, to not have direct DC connectivity between a charger's output side and a built-in battery. If it uses a lithium-based battery chemistry (a good guess in today's world, though I don't know), then all the more so.

@canina it IS a lithium battery, the older models used nimh, but this one uses Lithium (690). Unfortunately there's no way to get a hold of the schematic as there's no way irobot would provide it.

@dustytrash Even if you had access to a full and accurate schematic, that looks a whole lot like a multi-layer PCB to me, and it's definitely packed with surface-mount components including delicate ICs. Even if you had the knowledge, that's not something you "fix" with tools even most electronics enthusiasts would be likely to have at home; let alone if you had to go buy a power meter to determine the current draw of the charger, and are stumped once someone talks about power MOSFETs. Sorry.

This post is discussed on meta here.

PCB side 2 shows a lot of signs of a poor solder job. Check the top right corner of the last pic for example (looks like 0402). Probably they configured the placement machine poorly - there's too much solder everywhere and the potential for shorts looks extensive. Get some dirt on the board and anything can happen.

The fuse F1 on the top side lower right corner looks like it's been through a lot of heat, and the solder joints look a bit fishy too. These are supposed to be recoverable fuses, but I'd definitely replace that one still, though I can't tell what exact part it is. Though of course, if it is blown, the actual problem is likely a short elsewhere on the board.