I bought the EGO mower 3.5 years ago. At that time it came with the 56V 4ah battery. Last year the battery started acting odd where it wouldn't initially charge when placed on the charger. I would have to put it back in the mower and run it for a minute and then place it on the charger and eventually it would start charging. This year I got a couple of cuts and the battery started blinking as defective and would not charge. I debated on buying a new battery on a whole new mower due to price and availability. It seems tat home depot does not really carry the larger batteries and it take 2 weeks to get them in. I went with buying a new mower and grabbing the self propelled mower. I just got home and opened it up to grab the battery and get it charged. I placed the new battery on the old charger and it began charging. At that time I decided to place the old battery on the new charger to see what would happen and it began charging immediately. Now I don't know if the problem is the battery or the charger but they are not even 4 years old yet. At this point I now have to decide what to do and I am thinking about returning the new mower. I wish they had a discount for returning the older mowers for the purchase of a newer model. That would solve this problem and possibly keep customers coming back.