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<blockquote>The charger is supposed to output 20V-24V when the roomba is plugged in. However it's only showing 1.6V.</blockquote>

If this is really true, then there is no point going further.  The charger isn't working, the Roomba got discharged, and now wont run because it can't be recharged.

However, it's not clear what is really going on.  You say:

<blockquote>the picture just shows how I'm measuring the voltage. It's 0.4 when roomba is disconnected, 1.6V when connected.</blockquote>

But the picture seems to show something completely different:

![Image](https://electrical.codidact.com/uploads/reMEP3YznB8vetkaKetwsdqe)

There are a number of issues here:<ol>

<li>You haven't explained what that black thing is you're holding, or what its relevance is, so we can only ignore it.

<li>Your original picture is huge and shows a lot of blank wall.  Learn about "relevance", and then crop pictures accordingly.  There is no need to waste a full screen's area showing us the meter display.

<li>You don't show the actual connections to the charger, which would have been useful.  Frankly, I'm skeptical you know how to measure the charging voltage.  I need to see it to believe it.

<li>However, most importantly, <b>you're not actually measuring voltage</b>.  This is apparently a plug-in power meter.  It measures how much power something plugged in is drawing.  It plugs into an AC wall outlet, and provides its own outlet to the unit under test.  That lets it get between the AC power line and the unit, which allows it to measure the power drawn by the unit.

I can't even imagine how you thought this was a voltmeter.  Not only would this have been sold as a "power meter", but we can clearly see that the 0.4 you show is labeled with a "W", meaning Watts!

</ol>

So apparently the charger is drawing 0.4 <b>Watts</b> with nothing connected, and 1.6 <b>Watts</b> when the Roomba is supposed to be charging.  400 mW is a little high but still plausible with nothing connected.  However, 1.6 W is way too low to charge a Roomba.

Charging is definitely not working.  It's impossible to tell from that whether the fault is in the charger or the Roomba, or possibly (but unlikely) both.

Frankly, someone that thinks a power meter is a voltmeter and doesn't know that "W" means Watts shouldn't be inside electric equipment like that.  You're in over your head.  Close everything back up and hope you didn't break it more in the process of poking around in there.  There is nothing for you to see in here.  Move along.

What you <i>can</i> do is swap parts to determine whether you need a new charger or new Roomba.  Find someone with a working charger/Roomba combination.  Try your charger on their known working Roomba, and vice versa.  One of the combinations won't work, which tells you which of your units is broken.  Then go buy a replacement.