If your yard is flat, and not too large, one should be enough. Our yard is hilly and we have two for the job.Three would be better.
I have let mine run down to zero. And I have recharged when 3 of 4 green lights were on. Lithium-ion batteries are not like the old Ni-Cad batteries that were picky about when to recharge. Lithium batteries can be recharged at any level.
As long as it isn't in a freezing environment.
Hello Rgood, Yes, the RYOBI 40-Volt Lithium-Ion 5 Ah High Capacity Battery OP4050A is compatible with the RY40502. Thanks for asking! - Eve
It works fine in my ryobi chainsaw. I have Model # RY40502B
Sounds like you might have an internal short in your battery. Do you have a volt meter? You could check voltage. There is an 800 number you call call and they'll help you out. I've had good experience with the help line. Good luck.
There are a couple different 40v models. The 2ah, 4ah, 5ah, etc. The bigger the number the longer the run time. They are all interchangeable though. So use what you need.
Two things could be happening. One, the battery, durring the warm Summer months, could be just overheating and it reaches the automatic shut down tempurature before running out of power and this is normal for this battery. Two, One of the 20 - 18650 battery cells could be week and the voltage is dropping to low to run the lawn mower and it shuts down to protect the battery from becomming a 'Brick" if totally discharged. The voltage will start off high, after a fresh re-charge, at 42 volts, but, over the course of a "Run", the voltage will drop down to 34 volts. A fully charged 18650 lithium ion battery is 4.2 volts even though it is rated at 3.7 volts. There are two balanced string of 10 - 18650 cells in the Ryobi Battery pack. If one cell is week, the battery pack voltage could drop by 3.7 volts causing it to reach the 34 volt cut off after only partial use. The battery and charger needs to be tested at your local Home Depot Tool Rental and Service Center at you Local Home Depot Store. But before that, consider placing your 5 amp hour Ryobi Lithium batteries in a cool 45 degree F. place , like your refrigerator crisper, for 30 minuts before use so they start off cooler and run the lawn mower as usual to check run time. If it is just overheating, then starting cold will allow you to get the full run time of the battery and there most likely nothing wrong with it. However, if it still stops to soon then it might be one of the 18650 cells. Remember, your battery has a 3 year replacment warrenty, from date of purchase, so bring your original receipt with you.
Hi Tileman Thanks for your inquiry. The life expectancy is 3-5 years for a battery. Thanks for asking. Best Regards Thank you for contacting RYOBI.