To power my Ryobi 40V cordless electric mower I purchased two additional batteries. These batteries are made by a company called GERIT BATT and are 6 AH models. Currently, on Amazon these batteries are available for ~$80which is what I think that I paid for each earlier in the year.
The mower came with a Ryobi branded 4 AH battery and charger. Thus far it appears that the charger has no problem juicing the off brand batteries, which is a complaint that I read about from some reviewers. I will note that if I pull the battery off the charger when it claims to be full it runs for a shorter period of time compared to when I leave the battery on for some time after a full charge indication. Maybe there is some trickle charging going on or a quirk in the firmware of the charger. I do not know.
Below is a table showing all of my mowing this season and the times each battery lasted while mowing. I have been recording these results over the course of the lawn mowing season because I have found very little concrete analysis of battery life in cordless electric mowers. Batteries A and B are the GERIT BATT models while Battery R is the included Ryobi battery:
|Battery A||Battery B||Battery R|
|May 1||32||To complete||NA|
|May 8||34||To complete||NA|
|May 17||To complete||32||NA|
|May 22||40||To complete||NA|
|May 27||To complete||25:28||NA|
|June 5||26:42||24:15||To complete|
|June 8||To complete||38:51||NA|
|June 12||No time||No time||NA|
|June 21||To complete||37:25||NA|
|June 26||41:57||To complete||NA|
|July 2||39:44||To complete||NA|
|July 8||To complete||48:16||NA|
|July 13||45:02||To complete||NA|
|July 20||41:51||To complete||NA|
|July 28||37:05||To complate||NA|
|August 14||To complete||36:23||NA|
|August 28||To complete||39:04||NA|
After the first mowing I stopped using the self-propel feature of the mower believing it to use more electricity from the batteries than it was worth. The mower is quite light and my yard is not steep enough to really justify the extra juice. Plus, if I consider it a workout it’s better to make it more difficult. Right?
The biggest change in battery duration seems to be the dampness of the grass rather than the length. Early in the season we had a lot of spread out rain that kept everything fairly moist. Even mowing late in the day it would still be damp. Compared with later in the season when I let the grass grow long as the rain quit and the temperatures rose, mowing damp grass was just an energy suck. Check out June 1. It was like mowing through wet concrete.
You can see that the last month was a hot and dry period of time. I have really only mowed the lawn to even out some spots that grow long while large swaths of my yard stay at about 4-5” of grass height.
Regardless, it seems like mid-30 minute duration is consistent with some deviation to the high or low side dependent upon local conditions. Given that my yard is about two-thirds of an acre in size I would imagine that most suburban lots—about one quarter of an acre in size—could get buy with one 6 AH battery. The possibility of large emission reduction from replacing small engines with electric motors is gigantic.
Note: I bought the two GERIT BATT batteries with my own money from Amazon.com. I have received nothing in compensation for writing about or linking to the batteries.