Lawn mower batteries are junk even when new

[CleanSump]

Last time I had a similar problem it was a bad diode in the rectifier. The lights on that rider were AC so were only on when running. The ignition, starter, and kill switches were DC. New rectifier, battery stopped discharging when off.

 

[chemman]

Check to see what the AC ripple voltage is while the engine is running (and if your mower has headlights, turn them on as well). The higher the AC ripple voltage (ideally it should be less than 0.50 V) the less the battery is going to like it and the shorter the battery life.

 

[meep]

I’ve had excellent service from ariens oem sealed batteries. About $65 each. 5-6 years

 

[Pablo]

I’ve had excellent service from ariens oem sealed batteries. About $65 each. 5-6 years

Mine is at 5+ years now. Cranks like new. I think the alternator in the Kawa twin is fairly robust

 

[Learn Ya]

No matter what brand lawn mower battery I buy they all seem to last about 3 years

I agree. Anything beyond 3 years is a bonus for any OPE battery these days. I take good care of my batteries, but they still don't last like older batteries did. Prices go up, but quality goes down. It's seems to get worse every year.