So I have a Black and Decker CM1836 36v 9Ah lawn mower I’m considering upgrading to a Lipo Battery Pack. To the best of my knowledge this lawn mower is running on three 12v 9Ah batteries.
I’m wondering if I can just drop in this 36v 20Ah battery and replace the charger to make my mower better than new. this battery already has a BSM Board and a power supply for charging, I’m keenly concerned if I’m going about this wrong and if there is anyway to cut back on the cost as this would run about $310.
Any ideas or suggestions?
Here is a link to the standard replacement pack.
Not a bad idea. I wonder how large the battery is on those. I don’t want to spend the same amount of money and end up with a mower gets weak as quick as mine does now. looks like many of those run on a 2 to 3 Ah battery. I wonder if the gains from going lithium allow for much lower Ah battery packs to get the same run time? Might be grabbing too large of a cell for what I need.
The amp-hour rating for most lead-acid batteries is at some nonsense like C/30 or 30 hours to discharge since their original use was standby power for low-current applications such as alarm systems. As such, whenever you use them in high-current applications your yield will typically be less than half of faceplate. Modern lithium chemistries are typically rated at something close to 1C discharge rates, with high-rate power tool cells rated to more like 10-20C, so a 2-3 AH high-rate battery is more likely to deliver a long run time than a 7 A-H lead acid battery. YMMV and read the fine print first, natch.
Ahh, That makes since. I’ll try and do some more research, because the prices on the batteries go way down if I can bring my capacity down. I was seeing less than $50 for a 3Ah lithium rather than the 20Ah at $300+.
So some further reading lead to a forum post where a guy was trying to explain what your mentioned @ESmith
Tell me if this makes since.
SLA batteries are very efficient at delivering low power (1/20C or less), but become far less efficient when the demand for power is increased or temperatures drop.
A fully charged 12Ah SLA battery at 25 degrees C in good condition should be able to deliver 0.60Amps (12A/20) for 20 hours continuous, but if the same battery is completely discharged in one hour it will only deliver a continuous current of 7.20Amps (7.2Ah capacity not 12Ah).
If it is discharged at 12 Amps (1C) it will only last for approximately 35 minutes before it would be completely discharged, not the 60 minutes that you might expect.
If a 12Ah SLA battery is discharged at 36 Amps (3C) it will only last for approximately 10 minutes, which is equivalent to 6Ah!
A 12Ah lithium battery with a 3C discharge capability should be able to deliver the same 36 Amps of current for almost 20 minutes, and will also maintain a higher voltage throughout while doing so.
Reading the info from my lithium pack, I can’t find what the C rating is for the Ah. Same with the SLA battery, no infor on the C rating for the Ah. But if it is 20, which seems likely, I might be able to get by with a lithium that is 1/2 or 1/3 the capacity in Ah to get the same results, plus the lithium would have less voltage drop and would be able to be discharged to 85% vs the 50% limit of the SLA.
If you guys have any way to find the C rating on these batteries I’d love to find it out for sure. I find it amazing how we advertise numbers that don’t really mean anything without context. But, that is what you get when you are buying things for purposes you don’t fully understand.
Thinking of buying 2 of these and having them replaceable, rather than the 1 larger capacity. Gets 8Ah for $110, sound like a winner?
