Charging current only 70mA?

My 45 is drawing 85 mA at 80% charge, firmware v3.90. The 45S has a slightly smaller case, doesn't it? So perhaps both the battery and charging current are smaller. But failure to show 100% does sound worrying.

Do you get acceptable battery life? I run two or three times a week, I keep GPS and Bluetooth on all the time, and charge maybe every 3–5 days.

Yes similar battery life, and 45 does have a smaller battery. 

Just seems there's no real charging (0mA) once at 80% then after a while just changes to 100%

The 245 seems different, when between 80 and 100%, it charges in small bursts and periods of 0mA until at 100%. 

I've just checked mine again, from a nominal 80% charge. It started briefly at 100 mA, dropped to 85 mA, and has continued to fall in a more or less linear way. It's currently cycling between 5.1 and 5.4 mA. So it's clearly different from both your 45S and your 245!

On an unrelated note, it annoys me that the digital display of charge level is limited to steps of 20%, like the bar graph. Surely it wouldn't be hard to be a bit more precise?

I've now had a chance to redo a charge using a much better USB tester. Can see the current graph on the right - gets to about 6220 seconds and stops charging for a bit.

On the watch at this point, it shows '100%' which is between 80-100% thanks to the 45S only showing 20% increments?

At 6220s, it stopped charging for about 2 minutes, then at 6332s resumes charging at 70mA

Another 10 minutes later at 7100s, when it's dropped to 35mA it stops charging.

I think unplugging the watch when it first shows '100%' means you miss about 12 more minutes of charging. Maybe why I was getting less battery life too.

Also, using a power bank to charge can be a problem - if the power bank auto turns off once the watch gets to that first point where it stops charging.

Summary - just leave it 2 hours to charge if you want a full charge.

The power bank I use has the low power device mode - where you double press the button on it, then it stays charging for 2h and doesn't auto-off.

That's all really interesting. Nifty power meter you have there! Good point about power banks' tendency to shut off once the current falls to zero. Would all be much easier if Garmin would update the charge status display to 1% increments, I guess. Perhaps that's not as easy as it sounds on a device with very limited processing power.

Just for comparison, here is my Garmin 245M - charges at 200mA then around 90 min has decreased to around 50mA. 

At that point (around 7500 x-axis) the watch shows 100% - but is actually 100 as the 245 shows 1% increments.

It still charges a bit longer, levelling off at around 25mA.

Continuous charge, with no pause of 0mA.

That other behaviour is plain weird.