I’ve had my Black and Decker self-propelled electric lawn mower for a LONG time; I was an early adopter of cordless electric mowers and I love them: quiet, no gas fumes, good for the environment, virtually no maintenance. The only issues are: 1) it’s only 19″ wide so you have to do a bit more walking and 2) the lead acid battery is HEAVY (29lbs) and you need to remove it and charge it after each use.
Flash forward a decade or so and my lead acid batteries (I had two) have finally died; they won’t take a charge anymore. The electric lawn mower world has moved on to Lithium Ion batteries and you can’t buy a replacement anymore.
So the question is: fix or replace?
The battery is in a plastic shell that brings out the connectors, makes it water resistant, and keeps everything neat. There is an Anderson PowerPole-style connector to deliver power to the mower (high current) and a smaller polarized connector used for the (lower current) charger. The plastic shell is held together by 5 big screws and 4 small screws which I easily removed with a flat-head screwdriver. Inside were 3 Kung Long WP12-12 sealed lead acid (SLA) batteries (12V/12Ah each) connected in series to make 36V/12Ah. The batteries were dead, one was even cracked open. The batteries were taped together and stacked vertically in a T-shape; each battery is 5.94 x 3.86 x 3.74″ and weighs 8-9 lbs. They’re going to the recycling facility.
The options then are to:
Buy a new mower ($350-$600)
I’m a big fan of not throwing stuff out; it’s wasteful and bad for the environment. Moreover, most new mowers use 40V batteries that are only 3-5Ah (Black & Decker) to 6Ah (Ryobi). That’s not going to be nearly enough. The old 12Ah batteries were barely enough to do the whole lawn. Unsurprisingly, reviews of many new battery mowers say that battery life is too short.
Replace the SLA batteries ($83)
MightyMax maxes 12-12 batteries that are almost the same size and cost $27.67 each on amazon. This would be easiest, but then I’d still have that heavy battery pack and as I’ve gotten older, my back and I are much less fond of dragging 30lb batteries around.
Replace the SLA batteries with Lithium batteries
This I like. Lithium batteries have a much higher power density and so I can get similar power at dramatically lower weight. I know I can get Lithium Ion (LiIon) batteries that will easily fit in the shell, but I’d prefer LiFePO4 batteries which are similar, but safer and less prone to fire. The space inside the battery shell looks like it will comfortably fit a battery that is 7.75″ long, 3.5-3.75″ wide, and can be pretty tall. The challenge then is to find the right lithium battery.
One option would be to use three 12V/10Ah LiFePO4 batteries that are similarly sized such as the Goldenmate LFP-1210 (3 would cost $91.50 at amazon). These are 2.65lbs each and the manufacturer indicates 3 can be safely charged in series. All three batteries would weigh less than one of the SLA batteries. Goldenmate also has LFP-1212 (12Ah, $108 at amazon) and there are 12V/15Ah LiFePO4 batteries such as Sefepoder SP1215 (3 would cost $106 at amazon). Three of these batteries would weigh 10.5lbs so still a huge improvement over the SLA batteries plus more capacity! My main concern with any of these (aside from them being Chinese produced) is charging: I’d need a 36V (43.8V) LiFePO4 battery charger (at least another $30–$62 the more expensive one claiming to be being UL listed – also Chinese, I’m skeptical).
There are many 36V 10-14Ah lithium batteries available for eBikes and eScooters; many come with chargers. The challenge will be to find one that fits comfortably. I’ll post more details here once I’ve selected a battery solution.