What battery size does the John Deere 4020 use?
The John Deere 4020 commonly uses a 12-volt BCI Group 3ET battery. A current John Deere replacement is TY24341B, listed as 12V, 72Ah, 620 CCA, 3ET BCI. Early 24V-system 4020 tractors use two 12V batteries, while 12V-system tractors are listed with one 12V battery.
John Deere 4020 Battery Size: Group 3ET
The factory-style battery target is a 12V Group 3ET battery. Use two 12V batteries on original 24V-system tractors, or one 12V battery on 12V-system tractors.
75Ah listed spec; 72Ah on Deere TY24341B replacement
Common Deere Replacement
TY24341B-style 12V Group 3ET battery
Replacement CCA
620 CCA
24V-System Battery Count
2 batteries
12V-System Battery Count
1 battery
Charging System
Motorola alternator, 55 amps
Best simple answer: use a 12V Group 3ET battery. If your 4020 is still original 24V, it uses two 12V batteries.
John Deere 4020 12V vs 24V Battery Setup
4020 Setup
Battery Setup
Ground / Electrical Note
1964–1969 early system
Positive ground / floating 24V listed
24V-system tractors are listed with two 12V batteries
1969–1972 later system
Negative ground
12V-system tractors are listed with one 12V battery
Converted tractor
Depends on conversion
Check cable routing, starter, alternator, and battery box before buying
Important: identify whether your 4020 is original 24V, later 12V, or converted before changing batteries or cables.
Best Replacement Battery for a John Deere 4020
The clean factory-style replacement target is a 12V BCI Group 3ET battery. Deere’s TY24341B battery is listed as 12V, 72Ah, 620 CCA, 3ET BCI, which suits the narrow original-style 4020 battery boxes.
Replacement Check
What to Use
Original-style fit
12V Group 3ET battery
CCA target
620 CCA Deere replacement spec
Capacity target
72–75Ah
Terminal layout
Match existing cable routing and polarity
Converted 12V tractors
May use a different battery size if the tray, cables, and hold-downs were changed
What Battery Should You Buy for a John Deere 4020?
Best Factory-Style Choice
12V Group 3ET battery around 620 CCA and 72–75Ah.
Converted 12V Option
Group 31 may work only if your conversion has the right tray, cables, and hold-down setup.
Avoid
Guessing polarity, using loose batteries, mismatching cables, or wiring a 24V tractor like a normal 12V tractor.
Group 3ET vs Group 31 on a John Deere 4020
Battery
Use It When
Watch Out For
Group 3ET
You want original-style battery box fitment
Less common than truck batteries
Group 31
Your 4020 has a 12V conversion with modified fitment
Usually not a direct original battery-box fit
John Deere 4020 Battery Problems
Symptom
Likely Cause
Slow cranking
Weak battery, bad ground, corroded cables, voltage drop, or starter issue
Battery goes flat
Charging fault, parasitic drain, wiring problem, or bad alternator/generator setup
New battery still struggles
Poor cables, wrong battery setup, weak starter, or bad conversion wiring
Confusing cable routing
Original 24V system or old 12V conversion
John Deere 4020 Battery Replacement Tips
Tip
Why It Matters
Confirm the system first
24V and 12V 4020 tractors are not wired the same
Photograph the cables before removal
Prevents polarity and routing mistakes
Clean terminals and grounds
Bad connections make good batteries act weak
Use heavy battery cables
Undersized cables cause voltage drop and slow cranking
Secure the battery properly
Loose batteries damage terminals, trays, and wiring
John Deere 4020 Battery Questions
What battery size does a John Deere 4020 take?
The factory-style replacement size is a 12V BCI Group 3ET battery.
How many batteries does a John Deere 4020 have?
24V-system tractors are listed with two 12V batteries. 12V-system tractors are listed with one 12V battery.
What is the common John Deere 4020 replacement battery?
A common Deere replacement is TY24341B, a 12V, 72Ah, 620 CCA, 3ET BCI battery.
Is the John Deere 4020 12 volt or 24 volt?
Both exist. Early systems include positive ground/floating 24V listings, while later systems are negative ground 12V.
Can I use a Group 31 battery in a John Deere 4020?
Yes, but mainly on converted tractors with suitable battery box, cables, and hold-downs. Group 3ET is the better original-style fit.
Why does my John Deere 4020 crank slowly?
Common causes are weak batteries, poor grounds, corroded cables, voltage drop, starter problems, or incorrect conversion wiring.
John Deere 4020 Battery Size Summary
Battery group: BCI Group 3ET / 3ET BCI.
Battery voltage: 12 volts.
Common Deere replacement: TY24341B-style 12V, 72Ah, 620 CCA battery.
Listed capacity: 75Ah.
24V-system tractors: 2 batteries.
12V-system tractors: 1 battery.
Best owner answer: use Group 3ET for original-style fitment; check the wiring first if the tractor was converted.
Last checked: John Deere 4020 battery voltage, battery count, battery AH, early/late ground setup, charging amps, and Group 3ET replacement specs verified against TractorData and John Deere replacement battery listings.
