Aren't your tractor (and battery) under warranty?
If not, buy any 135Ah or bigger Ah capacity, similar dimensions and same polarity 12V battery. Look for battery with bigger cold crank amperage (880A or so) and longer warranty time.
Before replacement battery with new one check does original Akuma battery have enough electrolyte or is it dry. If is dry, add destilated water to proper level and recharge it by charger.
And most important thing:
Check battery connections and check voltage regulator of your generator, because (especially if battery is dry) it is main reason for battery failure. If regulator is bad, usually you will find corroded metal battery box from spilled electrolyte.
Check regulator following next procedure:
1. Start engine (and warm it up a little).
2. Connect voltmeter to battery connections
3. Measure voltage at idle engine RPM. It must be over 12.5V, and rise.
4. Run engine faster, step by step to 2000 rpm or full and read voltage.
5. Turn head lights on and measure again.
6. Voltage must be above 15V in any case (usually 14.4 V). If voltage go higher (over 15 up to 18V) replace regulator.
I had similar case on neighbour's
Zetor , but it can be common on any machine (not only Zetor's desease) ;-D
Hope this helps, Z.
