Project: Restoring A SONY WM-EX652 Walkman - Contact Cleaning For "Gum Bar" Battery.

I was trying to measure the amount of Play time having both batteries installed on the Walkman, as I saw some information saying that it should reach almost 40h.
In my case it was no longer than 10h, so at some moment I assumed the charger is not working and the "gum bar" is not charged.
I tried to use it without the AA battery extension and it was not working at all.
After measuring the "gum bar" battery I realized that something else is causing this low amount of Play time, maybe a broken or corroded contact.
I removed one of the face plates of the Walkman, as you can see below:

After removing the screws marked with red color I was able to reach the battery housing:

After a closer look I saw the corroded contact:

In order to clean it I used an old tooth brush and contact cleaner, below you can see the result:

Now the unit is working on both batteries, used together or separated. What is left to be done is to count how many tapes I will be able to listen without charging the batteries.

TEAC A-3440: Data Information And Technical Characteristics.

Specifications:

• Track System: 4-Channel Multi-Track Simul-Sync;
• 3 Motors: 
• 1 DC-Servo Capstan Motor;
• 2 Eddy Current Induction Reel Motors;
• 3 Heads:
• Erase;
• Record/Sync;
• Playback;
• Reel Size:
• 26.5 cm (10-1/2");
• 18 cm (7");
• Tape Speed:
• 38 cm/s (15 ips)  (±5%);
• 19 cm/s (7-1/2 ips) (±5%);
• Wow and Flutter (NAB Weighted):
• 0.04% at 15 ips;
• 0.06% at 7-1/2 ips;
• Frequency Response (overall):
• 25 - 24000 Hz (±3dβ/0 VU: 40 - 22000Hz) at 15ips;
• 25 - 22000 Hz (±3dβ/-10 VU: 40 - 20000Hz) at 7-1/2ips;
• Signal-to-Noise Ratio (overall): 55dβ (3% THD level, weighted);
• Harmonic Distortion (overall): 0.8% at normal operating level;
• Stereo Channel Separation:45dβ at 1 kHz;
• Rewind/Fast Forward Time: 140s for 1800ft;
• Inputs:
• 4 Line: 60mV/50kΩ;
• 4 Mic: 0.25mV (-72dβ)/600Ω or more;
• Outputs:
• 4 Line: 0.3V/load impedance: 10kΩ or more;
• 1 Headphone Jack: 8Ω;
• Power Requirement:
• 100/117/220/240V AC, 50/60Hz (EX Model);
• 220V AC, 50Hz (EUR Model);
• 240V AC, 50Hz (UK/AUS Model);
• 117V AC, 60Hz (USA/CND Model);
• Power Consumption: 125W;
• Dimensions (W x H x D):
• 445 x 523 x 235mm;
• 17-1/2" x 20-1/2" x 9-1/4"
• Weight: 25kg (55lbs) net;
• Supplied Accessories:
• Input Output Connection Cords;
• RE-1002 Empty Reel;
• NAB Reel Hub Adapters;
• Spicing Tape;

SONY WM-EX652: Data Information And Technical Characteristics.

Supplied Accessories:

• Battery Case;
• Stereo Headphones with Remote Control;
• Clip (which I don't have, I don't know how it looks like);
• Battery Charger;
• AC Plug Adapter (except European, Arabian and Korean Models);
• Rechargeable Battery (NC-6WM, 1.2V, 600mAh, Ni-Cd);
• Carrying Pouch (don't have it either);
• Rechargeable battery carrying case;

General:

• Power Requirements:
• 1.5V;
• Rechargeable Battery;
• One R6 (AA) Battery;
• Dimensions (W/H/D):
• 108.9 x 79.6 x 23.9mm;
• Weight:
• 140g;
• 225g rechargeable battery, headphones with remote control and cassette inclusive;

Tape Section:

• Frequency Response (Dolby NR Off):
• Playback: 20 - 18000Hz;
• Output:
• Headphones;
• Load Impedance: 8 - 300Ω;
• Power Output:
• 5mW + 5mW (16Ω);