Macbook battery bar showing as red; battery % jumps around; battery condition normal; out of US charging

I've been in Europe since 7/5. I've been charging my 2015 macbook pro (purchased in the US) in the UK from 7/5-7/11 and in Italy from 7/11-current. I use a power adapter (not a converter) since the US prongs don't fit in the outlets in the UK or Italy. I don't use a converter, and the European outlets are all 220v, but this should be compatible with a macbook.

Today, I just noticed that my battery % has been jumping up and down a bit. I also noticed that the battery bar is red despite having over 20%. I have never seen this happen before, so I'm wondering if my battery got damaged somehow.

The information in System Information is shown below, and it states that my battery is functioning normally. Any ideas what may be happening?

Battery Information:

  Model Information:
  Serial Number:    ---
  Manufacturer: DP
  Device Name:  ---
  Pack Lot Code:    0
  PCB Lot Code: 0
  Firmware Version: 702
  Hardware Revision:    1
  Cell Revision:    3224
  Charge Information:
  Charge Remaining (mAh):   1130
  Fully Charged:    No
  Charging: No
  Full Charge Capacity (mAh):   4598
  Health Information:
  Cycle Count:  837
  Condition:    Normal
  Battery Installed:    Yes
  Amperage (mA):    -1275
  Voltage (mV): 10962

System Power Settings:

  AC Power:
  System Sleep Timer (Minutes): 1
  Disk Sleep Timer (Minutes):   10
  Display Sleep Timer (Minutes):    10
  Wake on AC Change:    No
  Wake on Clamshell Open:   Yes
  Wake on LAN:  No
  AutoPowerOff Delay:   28800
  AutoPowerOff Enabled: 1
  DarkWakeBackgroundTasks:  1
  Display Sleep Uses Dim:   Yes
  GPUSwitch:    2
  Hibernate Mode:   3
  High Standby Delay:   86400
  PrioritizeNetworkReachabilityOverSleep:   0
  ProximityDarkWake:    1
  Standby Battery Threshold:    50
  Standby Delay:    10800
  Standby Enabled:  1
  TCPKeepAlivePref: 1
  Battery Power:
  System Sleep Timer (Minutes): 1
  Disk Sleep Timer (Minutes):   10
  Display Sleep Timer (Minutes):    2
  Wake on AC Change:    No
  Wake on Clamshell Open:   Yes
  AutoPowerOff Delay:   28800
  AutoPowerOff Enabled: 1
  Current Power Source: Yes
  DarkWakeBackgroundTasks:  0
  Display Sleep Uses Dim:   Yes
  GPUSwitch:    2
  Hibernate Mode:   3
  High Standby Delay:   86400
  ProximityDarkWake:    0
  Reduce Brightness:    Yes
  Standby Battery Threshold:    50
  Standby Delay:    10800
  Standby Enabled:  1
  TCPKeepAlivePref: 1

Hardware Configuration:

  UPS Installed:    No

AC Charger Information:

  Connected:    No
  Charging: No

I would start by resetting the System Management Controller (SMC) which is responsible for power management and controlling the thermal environment of your Mac. Typically this covers things like interpreting and responding to various sensors, battery charging, sleep/wake/hibernation, the power button and restarts/shutdowns, LED indicators, and so on.

To reset the SMC on your model MBP follow these steps:

1. Fully shut down your MBP
2. Press ShiftControlOption on the left side of the built-in keyboard, and press the power button at the same time
3. Keep holding these down for at least 10 seconds before letting go
4. Power up the MBP again

Once you've done this keep an eye on your battery status to see if you notice any changes.

As an aside, I note your battery has a cycle count of 837. To put this into perspective, your MacBook Pro battery has a life expectancy at or around 1000 cycles. It's not uncommon for batteries to exceed or fall short of this number; it's just an estimation of how long it can last. You can refer to Determine battery cycle count for Mac notebooks on Apple's website for more info.

As your battery condition is listed as Normal I wouldn't be too concerned about the cycle count yet, but you may need to think about a battery replacement in the not-too-distant future.

You may also like to take a look at How to reset the System Management Controller (SMC) on your Mac. It provides more info on what the SMC does, when you to reset it, etc.